Electric heating pad

ABSTRACT

An electric heating pad for warming a patient. The electric heating pad may be a heated underbody support, heated mattress or heated mattress overlay. An embodiment of the heating pad includes a flexible sheet-like heating element including an upper edge, a lower edge, and at least two side edges. The heating pad may also include a shell covering the heating element and comprising at least two sheets of flexible material (e.g., two sheets may be one sheet folded over to form at least two sheets). The two sheets of flexible material may be coupled together about the edges of the heating element by a weld. The material of the two sheets may include urethane. In some embodiments, a catalyst to accelerate hydrogen peroxide decomposition is coated on or impregnated into an element within the shell, or on the interior surface of the shell.

This application is a continuation of U.S. application Ser. No.16/246,504, filed Jan. 13, 2019, which is a continuation of U.S.application Ser. No. 14/842,533, filed Sep. 1, 2015, now U.S. Pat. No.10,201,935 issued Feb. 12, 2019, which is a continuation-in-part of U.S.application Ser. No. 14/287,292, filed May 27, 2014, now U.S. Pat. No.10,506,668 issued Dec. 10, 2019, which is a continuation of U.S.application Ser. No. 13/460,368, filed Apr. 30, 2012, now U.S. Pat. No.8,772,676 issued Jul. 8, 2014, which is a continuation of U.S.application Ser. No. 12/050,806, filed Mar. 18, 2008, now U.S. Pat. No.8,283,602 issued Oct. 9, 2012, which claims priority to U.S. ProvisionalPatent Application No. 60/895,736, filed Mar. 19, 2007. This applicationis also a continuation-in-part of three pending U.S. applicationsincluding: U.S. Provisional Patent Application No. 62/079,076, filedNov. 13, 2014; U.S. application Ser. No. 13/422,279, filed Mar. 16,2012; and U.S. application Ser. No. 14/683,915, filed Apr. 10, 2015. Theentire contents of all of these applications are incorporated herein byreference.

TECHNICAL FIELD

The present invention is related to heater assemblies including heatingor warming blankets or pads, and more particularly to those includingelectrical heating elements.

BACKGROUND

It is well established that surgical patients under anesthesia becomepoikilothermic. This means that the patients lose their ability tocontrol their body temperature and will take on or lose heat dependingon the temperature of the environment. Since modern operating rooms areall air conditioned to a relatively low temperature for surgeon comfort,the majority of patients undergoing general anesthesia will lose heatand become clinically hypothermic if not warmed.

There have been many attempts at making heated blankets and pads,including pads in the form of heated underbody supports, heatedmattresses and heated mattress overlays for therapeutic patient warming.Therapeutic patient warming is especially important for patients duringsurgery. It is well known that without therapeutic intra-operativewarming, most anesthetized surgical patients will become clinicallyhypothermic during surgery. Hypothermia has been linked to increasedwound infections, increased blood loss, increased cardiac morbidity,prolonged ICU time, prolonged hospital stays, increased cost of surgeryand increased death rates.

Over the past 15 years, forced-air warming (FAW) has become one of the“standard of care” for preventing and treating the hypothermia caused byanesthesia and surgery. FAW consists of a large heater/blower attachedby a hose to an inflatable air blanket. The warm air is distributed overthe patient within the chambers of the blanket and then is exhaustedonto the patient through holes in the bottom surface of the blanket.

Although FAW is clinically effective, it suffers from several problemsincluding: a relatively high price; air blowing in the operating room,which can be noisy and can potentially contaminate the surgical field;and bulkiness, which, at times, may obscure the view of the surgeon.Moreover, the low specific heat of air and the rapid loss of heat fromair require that the temperature of the air, as it leaves the hose, bedangerously high—in some products as high as 45° C. This posessignificant dangers for the patient. Second and third degree burns haveoccurred both because of contact between the hose and the patient'sskin, and by blowing hot air directly from the hose onto the skinwithout connecting a blanket to the hose. This condition is commonenough to have its own name—“hosing.” The manufacturers of forced airwarming equipment actively warn their users against hosing and the risksit poses to the patient.

To overcome the aforementioned problems with FAW, several companies havedeveloped electric warming blankets. Some of these warming blanketsemploy flexible heaters, the flexibility of which is desirable tomaintain when employing the blankets. In many cases, an electric warmingblanket employs a shell for holding the heater and for serving otherpurposes. For example, in some cases the shell includes layers formed ofa substantially water impermeable material to help prevent fluid damageto the heater. Also, when these heaters are used for patient or othercare, especially in the operating room, the shell can protect thepatient and others in the vicinity from electric shock hazards. Inaddition to often providing a seal around the heater, the shell oftencontains a fastening mechanism that must reliably attach the heater tothe shell to prevent electrical shorting across the heater duringfolding of the electric warming blanket.

Because the seals of the shell must be very reliable, the seals havetraditionally been adhesive seals that are reinforced with combinationsof sewing, rivets, and grommets. Sewing stitches, rivets, and grommetsall share one characteristic—they all perforate the material layers tocreate a mechanical linkage between the layers.

While such a reinforced bond may be desirable for strength, it cancreate additional problems when used during surgery or medicalprocedures. For example, heated blankets placed over a patient during asurgery or medical procedure are frequently soiled with waste blood orother body fluids. The fluid waste can saturate the stitching and thendry and accumulate in the thread or the stitch holes. If rivets orgrommets are used for reinforcement, additional crevasses are introducedthat can trap waste fluids. When the outer shell of the blanket iscleaned by hospital personnel, it is nearly impossible to clean theresidual contaminating materials out of the holes, crevasses, and/orstitches. Therefore, the stitching holes and thread, the grommets,rivets and snaps can all become sources of microbial contaminationbecause they cannot be thoroughly cleaned and disinfected.

Prior to the 1990's, warm water mattresses were commonly used. The warmwater mattresses went out of common use because they were relativelystiff and inflexible. The stiff water mattress negated any pressurerelief that the underlaying support mattress may have provided. As aresult, the combination of pressure applied to the boney prominences andthe heat from the warm water mattress both reduced blood flow andaccelerated metabolism, causing accelerated ischemic pressure injuriesto the skin (“bed sores”). Additionally, the warmed water recirculatingin the warming system was well known to be grossly contaminated withbacteria, which was especially important when a leak occurred. As aresult, warm water mattresses are rarely used today.

Historically, electrically heated pads and blankets for the consumermarket have been made with resistive wire heaters. Wire-based heatershave been questionably safe in consumer use. However, in the operatingroom environment with anesthetized patients, hot spots caused by thewires in normal use and the failure mode of broken heater wiresresulting in sparking, arcing and fires are totally unacceptable.Therefore, resistive wire-based heaters are not used in the operatingroom today.

Since the mid 1990's, a number of inventors have tried unsuccessfully tomake effective and safe heated mattresses for operating room use, usingflexible, sheet-like electric resistance heaters. The sheet-like heatershave been shown to be more effective in warming the patients because ofthe even heat production and generally do not cause arcing and sparkingwhen they fail.

Some existing devices employ sheet-like heaters using a polymeric fabricthat has been baked at high temperature until it becomes carbonized andis thus conductive of electricity. The carbonization process makes thefabric fragile, and therefore, it may be laminated between two layers ofplastic film or fiber-reinforced plastic film for stability andstrength. The lamination process results in a relatively stiff, althoughsomewhat flexible, non-stretching, non-conforming heater. The metal foilbus bars are attached to the heater material with an “electricallyconductive adhesive or bonding composition . . . ” and then encapsulatedwith polyurethane-coated nylon fabric. The result is a stiff andrelatively inflexible bus bar.

Clearly, there is a need for conductive fabric heaters for use intherapeutic heated mattresses that are highly flexible, stretchable inat least one direction and durable without needing lamination tostabilize or protect the heater fabric. There is also a need for bus barconstruction that does not result in thick, stiff, inflexible areasalong the side edges of the heater. Then, maximally effective and safetherapeutic heated mattresses need to be designed using the stretchable,durable fabric heaters.

In addition to patient warming during surgery, and as known to thoseskilled in the art, modern surgical techniques typically employ radiofrequency (RF) cautery to cut and coagulate bleeding encountered inperforming surgical procedures. Every electrosurgical generator systemmay have an active electrode that is applied by the surgeon to thepatient at the surgical site to perform surgery and an electrical returnpath from the patient back to the generator. The active electrode at thepoint of contact with the patient may be small in size to produce a highcurrent density in order to produce a surgical effect of cutting orcoagulating tissue. The return electrode, which carries the same currentas the active electrode, may be large enough in effective surface areaat the point of communication with the patient such that a low densitycurrent flows from the patient to the return electrode. If a relativelyhigh current density is produced at the return electrode, thetemperature of the patient's skin and underlying tissue will rise inthis area and can result in a patient burn.

Return electrodes have evolved over the years from small 12×7-inch, flatstainless steel plates coated with a conductive gel that were placedunder the patient's buttocks, thigh, shoulders, or any location wheregravity could ensure adequate contact. The next development was flexiblefoam-backed electrodes. These flexible electrodes are about the samesize as the stainless steel plates and are coated with a conductivepolymer. They have an adhesive border so that they remain attached tothe patient without the aid of gravity.

Described as early as 1938 and first introduced into the surgical marketin 1960, capacitively coupled return electrodes offer an alternative toconductive return electrodes. Unlike conductive electrodes, whichinvolve direct patient contact, a capacitively coupled electrode isplaced close to, but not touching, the patient. It is separated from thepatient by a dielectric barrier—that is, a layer of insulating material.This allows the electrode to form a capacitor with the patient. Acapacitor is an electrical circuit element used to store a chargetemporarily. In use, this type of electrode induces a current flowacross the electrode-patient capacitor such that electricity is safelyreturned from the patient to the electrosurgical unit across adielectric insulator layer, allowing the desired surgical effect at thesurgical site.

A capacitively coupled return electrode consists of a single conductiveplate, fabric or film that is encased in a dielectric material. Theinsulating material does not permit the charge to flow through theelectrode to the patient. When placed in close proximity to each other,the conductive plate and the patient become capacitively coupled. Theirseparation is maintained by the electrode's insulating material, whichforms a dielectric barrier between them. For example, a large flat sheetof conductive material that covers a portion of the operating table maybe the electrode and the dielectric barrier may consist of plastic film,linens, cushions or other materials that may be placed between thepatient and the electrode.

When the active electrode is applied at the surgical site, theelectrosurgical unit induces an oscillating radio frequency (RF) voltagethrough the surgical site and between the patient and the returnelectrode's conductive plate. As this occurs, several events take placesimultaneously. First, an electrical charge accumulates and diminishesin cycles, both on the surface of the patient over lapping the returnelectrode and on the electrode's capacitive plate, in equal and opposingpolarities. Second, the dielectric material becomes polarized: anelectrical charge will not move through it. Finally, as the electricalcharge moves to and from the surface of the patient's skin, there is aloss of energy that produces a minimal amount of heat within the skin(as happens with a conductive return electrode).

If the dielectric is thin, meaning that the patient and the returnelectrode are close together—for example less than 2 mm—the capacitivecoupling is very efficient. If the distance between the patient and theelectrode increases, the efficiency of the coupling decreases.Therefore, minimizing the distance between the patient and the electrodemay be desirable. The ability of this design to minimize the distance ofboth the heater and the grounding electrode from the patient may beparticularly desirable with small pediatric patients who have minimalsurface area contacting the support surface.

There is some concern that an unnoticed, accidental hole in theelectrode's dielectric material could provide a conductive contact withthe patient over a very small area, causing a large concentration ofcurrent to flow in a small area and to burn the patient. In some cases,thick layers of “self-sealing” gel material have been interposed betweenthe electrode and the dielectric material to prevent a conductivepathway from occurring in the event of a hole in the dielectricmaterial. The gel material is heavy and cumbersome.

Capacitive coupling electrodes generally have been mattress overlays,which are inconvenient, involving extra cleaning. Additionally, they areusually non-stretching conductive fabric—for example, woven nylonembedded into a heavy, cumbersome gel pad—which reduces theeffectiveness of the pressure-reducing mattress of the surgical table.The conductive silver coating on the fabric electrode also diminishesradiolucency to x-rays, causing x-rays that are shot through themattress to be grainy or distorted.

The location of the capacitive coupling grounding electrode under thepatient is in direct competition for space with heated underbody warmingpads and mattresses commonly used in surgery. Heated underbody warmingpads and mattresses also work optimally when in close contact with thepatient's skin. Therefore, both of these safety technologies may notperform optimally when used simultaneously as two separate devices sinceseemingly only one or the other can be optimally placed adjacent thepatient's skin.

Clearly, there is a need for improvement by combining the capacitivecoupling electrode with the heated underbody warming system. However,simply combining the two technologies into a single shell could producea laminated structure that would be less stretchable, less flexible andless accommodating—further preventing the patient from sinking optimallyinto the support mattress and increasing the risk of pressure ulcers.

Combining the capacitive coupling electrode with the heated underbodywarming system in a single layer of stretchable, flexible material thatcan serve as a heater and grounding electrode simultaneously wouldprevent the problems resulting from a two-layer laminate structure andwould reduce the cost and complexity of manufacturing.

Accordingly, there remains a need for heated blankets, shells and padsfor flexible heaters that are readily and thoroughly cleanable. Therealso remains a need for improvements in electrosurgical grounding forsurgery. In particular, there is a need for devices including thesefeatures that also offer pressure relief and prevent bed sores.

Various embodiments of the invention described herein solve one or moreof the problems discussed above in addition to other problems that willbecome apparent.

SUMMARY

Certain embodiments of the invention include a heater assembly such asan electric heating blanket or pad including a flexible sheet-likeheating element and a shell. The shell covers the heating blanket or padand includes two sheets of flexible material welded together. In someembodiments the weld couples the sheets together about the edges of theheating element. In some embodiments, the weld couples the sheets aboutthe edges of the sheets. Although the heating blanket or pad isdescribed as having two sheets welded together, as one of ordinary skillin the art would consider, the two sheets could be formed from one sheetfolded over on itself to form the two different sheet layers.

In some embodiments, the heated blanket or pad includes a groundingelectrode for electrosurgical equipment. These capacitive couplinggrounding electrodes are well known in the arts. In some embodiments,the capacitive grounding electrode is the conductive heater material(e.g., heating element) that is simultaneously incorporated into thecircuits of both the heater/power supply/controller and theelectrosurgical unit. In some embodiments, the simultaneous use of theheating element material for heating and grounding allows bothtechnologies to be positioned optimally close to the patient's skin forthe maximum efficiency of each therapy.

In some embodiments the grounding electrode is the heating element orheater assembly. The heating elements of the instant inventions arepreferentially made of conductive or semi-conductive fabrics or films.The conductive or semi-conductive properties of the heating elementmaterial allow it to double as a grounding electrode. The heatingelement/grounding electrode may advantageously be made of asemi-conductive polymer such as polypyrrole. It is well known that theelectrical properties of polypyrrole make it a suitable material forabsorbing radar. Polypyrrole has been used as a radar absorbing materialin “stealth” aircraft and watercraft. The microwave frequencies of radarare not unlike the RF frequencies used in electro-surgery. Thesemi-conductive properties of polypyrrole that lead to preferentialabsorption of high frequency electro-magnetic waves are in contrast toelectrically conductive properties of composites made from powdered orvaporized carbon or metals. Metal powder particles deposited on thesurface of a fabric material may conduct electricity, but do notpreferentially absorb high frequency EM waves. Thin metal coatings mayallow “tunneling” of some of the EM waves through the spaces between theparticles, allowing the waves to pass right through the material withoutbeing absorbed. If the metallic coating is thick, “tunneling” may beprevented, but then reflection and scattering of the EM waves may resultin decreased absorption. Therefore, the silver-coated fabrics that havebeen used in many past electrosurgical grounding pads are seemingly notpreferential RF energy absorbers. A semi-conductive polymer such aspolypyrrole is advantageous in that it is a preferential RF energyabsorber.

In other embodiments, the grounding electrode is a separate layer ofmaterial positioned near and parallel to the heating element. In thiscase, the grounding electrode may advantageously be made of asemi-conductive polymer such as polypyrrole irrespective of what thematerial the heating element is made from.

In some embodiments, the grounding electrode is a separate layer ofmaterial, and there is no heating element. In these cases, the groundingelectrode may advantageously be made of a semi-conductive polymer suchas polypyrrole.

In some embodiments, the grounding electrode wire is connected directlyto the grounding electrode (heating element) material. This connectionhas been used previously and works acceptably as long as the groundingelectrode is made of highly conductive material such as silver-coatednylon fabric. The very low resistance to flow through the silver-coatedfabric allows the grounding wire to be connected to the electrode in anylocation.

In some embodiments, the grounding electrode wire is connected to one ofthe heating element bus bars. Connecting the grounding wire to the busbar is advantageous when the grounding electrode material is a resistiveheater material that adds resistance to the circuit. A grounding wireconnected to one end of the heater, rather than to a bus bar, wouldcreate a situation wherein the electrical resistance to current flowwould be significantly greater for current originating at the far end ofthe heater compared to current originating at the end of the patientclosest to the wire connection. This situation would cause more of thecurrent to flow through the parts of the patient closest to the wireconnection and possibly create an unsafe condition. In contrast, sincethe bus bar runs substantially parallel to the long axis of the patient,along an edge of the grounding electrode, the distance from the bus barto the patient is relatively equal along its length, and the resistanceto the current flow caused by the heater material is thus substantiallyequal along the entire length of the patient that is contacting thegrounding electrode, creating a safe condition.

In some embodiments, the output electrical currents of both theheater/power supply/controller and the electrosurgical generator are“floating,” meaning that they are not referenced to earth (ground) andhave no electrical potential to earth (ground) or to each other. In someembodiments, the output electrical currents of both the heater/powersupply/controller and the electrosurgical unit are “isolated,” meaningthat they have no electrical potential to and are not referenced toearth (ground). In some embodiments, the output electrical current ofthe heater/power supply/controller is a direct current. In someembodiments, the output electrical current of the heater/powersupply/controller is low voltage, meaning equal to or less than 48 voltsDC.

In some embodiments, the temperature sensor of the heated blanket or pad(e.g., underbody warming system, or heated underbody support) is locatedon the heater assembly, so that it senses the temperature of the heaterassembly in contact with the patient. The temperature sensor thus alsoserves as a safety sensor, decreasing power to the heater assemblyexcess heat buildup under the patient from the electrosurgicalgrounding. The heater controller will alarm if the heater temperatureexceeds a safe temperature for heating the skin whether the heating isdue to the effect of the heater assembly or the capacitive grounding.

In some embodiments, one or both sides of the heating element materialare coated with a thin layer of flexible, stretchable elastomericmaterial such as rubber or silicone. Preferably the elastomeric materialis stretchable, flexible, self-sealing and protects the individualfibers of the heating element from moisture damage. This coating ofelastomeric material interposed between the electrode and the dielectricmaterial layers serves as second, redundant dielectric layer should aninadvertent hole be put into the outer shell. The redundant dielectriclayer would prevent direct electrical coupling between the patient andthe electrode material that could cause a burn.

In some embodiments, the heater/grounding electrode is encased in aflexible dielectric shell that can be flexed up along the sides of thesmall pediatric patient to improve both the heat transfer and capacitivecoupling effects. Flexing the heater/grounding electrode places more ofthe surface area in close contact with the patient's skin for optimalperformance of both heat transfer and capacitive grounding.

In some embodiments, the conductive or semi-conductive material ispolypyrrole. In some embodiments the compressible material includes afoam material and in some embodiments it includes one or more air filledchambers. For example, in some embodiments of the heater assembly may bea blanket or pad that includes a water resistant shell encasing theheater assembly, including an upper shell and a lower shell that aresealed together along their edges to form a bonded edge, with the heaterassembly attached to the shell along one or more edges of the heaterassembly. In some embodiments, the heated pad (e.g., heated underbodysupport pad) also includes a water resistant shell encasing the heaterassembly, including an upper shell and a lower shell that are sewntogether along their edges to form a sewn and bonded edge. In someembodiments, the heating element has a generally planar shape when notunder pressure, is adapted to stretch into a 3 dimensional compoundcurve without wrinkling or folding while maintaining electricalconductivity in response to pressure, and to return to the samegenerally planar shape when pressure is removed.

Maximal patient warming effectiveness is achieved by maximallyaccommodating the patient into the mattress. In other words, maximizingthe contact area between the patient's skin and the heated surface ofthe mattress. The heater and foam (compressible material) or airbladders of the mattress may be easily deformable to allow the patientto sink into the mattress. This accommodation maximizes the patientsskin surface area in contact with the mattress and heater, whichminimizes the pressure applied to any given point. It also maximizes thesurface contact area for heat transfer and maximizes blood flow to theskin in contact with the heat for optimal heat transfer. Theaccommodation of the patient into the mattress may not be hindered by astiff, non-conforming, non-stretching, hammocking heater. Additionally,the heater should be near the top surface of the mattress, in thermallyconductive contact with the patient's skin, not buried beneath thicklayers of foam or fibrous insulation.

In some embodiments, the compressible material comprises one or moreflexible air filled chambers. In some embodiments, the compressiblematerial is a foam material. The heater assembly may be attached to thetop surface of the layer of compressible material. In some embodiments,the heated underbody support includes a water resistant shell encasingthe heating element/heater assembly and having an upper shell and alower shell that are sealed together along their edges to form a bondededge. In some embodiments, one or more edges of the heater assembly maybe sealed into the bonded edge. In some embodiments, the heater assemblyis attached to the upper layer of water resistant shell material. Insome embodiments, the heater assembly is attached to the shell onlyalong one or more edges of the heater assembly. In some embodiments, theheated underbody support also includes an electrical inlet, wherein theinlet is bonded to the upper shell and the lower shell and passesbetween them at the bonded edge.

Electrically heated mattresses are compressible and accommodating, thusthe patients sink into the mattress and more body surface area isrecruited to help support the weight of the patient. If the proper foammaterials are chosen, virtually the entire posterior surface of thepatient contacts the mattress. However, even with the added contactsurface area, these mattresses are incapable of transferring enough heatto maintain patient normothermia, especially in pediatric patients.

Small pediatric patients have another problem with accommodation intothe foam. Their light weight prevents them from sinking into the foammattress. Therefore expecting the depression into the foam caused by thepatients weight to form the foam around the patient's body therebyincreasing the contact with their side surfaces, is clearly impossiblein pediatrics.

There is a need for a surgical patient warming mattress that has agreater heat transfer capacity. Since the contact temperature cannot beincreased without causing burns, seemingly the only option to increaseheat transfer is to increase the body surface contact area. The increasethe body surface contact area also increases the efficiency of thecapacitive coupling of the grounding electrode in the mattress. Theinstant invention effectively increases the body surface contact area bysubstantially separating the patient support functions of the mattressfrom the patient warming and electrosurgical grounding functions of themattress. By separating these two functions, each can be maximizedindependently. At the same time, both of the functions are stillsimultaneously maintained, to provide a safe and effective heatedsupport surface for surgery.

BRIEF DESCRIPTION OF THE DRAWINGS

The following drawings are illustrative of particular embodiments of thepresent invention and therefore do not limit the scope of the invention.The drawings are not to scale (unless so stated) and are intended foruse in conjunction with the explanations in the following detaileddescription. Embodiments of the present invention will hereinafter bedescribed in conjunction with the appended drawings, wherein likenumerals denote like elements.

FIG. 1 is a top plan view of a heating blanket or pad, according to someembodiments of the present invention.

FIG. 2A is a plan view of a flexible heating blanket or pad subassemblyfor a heating blanket, according to some embodiments of the presentinvention.

FIG. 2B is an end view of some embodiments of the subassembly shown inFIG. 2A.

FIG. 3A is a top plan view of a heating element assembly, according tosome embodiments of the present invention, which may be incorporated inthe blanket or pad shown in FIG. 1 .

FIG. 3B is a section view of the temperature sensor assembly of FIG. 3A.

FIG. 4A is a top plan view of a heating element assembly, which may beincorporated in the blanket or pad shown in FIG. 1 .

FIG. 4B is a cross-section view through section line 4B-4B of FIG. 4A.

FIG. 5A is a cross-section of a shell containing a heating elementaccording to some embodiments of the present invention.

FIG. 5B is a top plan view of the shell of FIG. 5A.

FIG. 6 is a cross-section of a shell containing an air pocket accordingto some embodiments of the present invention.

FIG. 7A is a top plan view of a shell having straps according to someembodiments of the present invention.

FIG. 7B is a cross-section of the shell of FIG. 7A.

FIG. 8 is a cross-section of a shell containing a heating elementsecured to the shell according to some embodiments of the presentinvention.

FIG. 9A is a top plan view of a shell containing reinforced hangerpoints according to some embodiments of the present invention.

FIG. 9B is a cross-section of the shell of FIG. 9A.

FIG. 10A is a cross-section of a shell containing a heating element,including an attachment point secured to the shell according to someembodiments of the present invention.

FIG. 10B is a cross-section of a shell containing a heating element,including an attachment point secured to the shell according to someembodiments of the present invention.

FIG. 11 is a cross-section of two ends of a shell containing a heatingelement, including a securing magnet.

FIG. 12 is a cross sectional view of a heater assembly undergoingdeformation in accordance with embodiments of the invention.

FIGS. 13, 13A and 13B are cross sectional views of a heated mattressoverlay or pad in accordance with embodiments of the invention.

FIG. 14 is a cross sectional view of a heated mattress overlay or pad inaccordance with embodiments of the invention.

FIG. 15 is a cross sectional view of a heated mattress overlay or pad inaccordance with embodiments of the invention.

FIG. 16 is a cross sectional view of a heated mattress overlay or pad inaccordance with embodiments of the invention.

FIG. 17 is a cross sectional view of a heated mattress overlay or pad inaccordance with embodiments of the invention.

FIG. 18 is a cross sectional view of a heated mattress overlay or pad inaccordance with embodiments of the invention.

FIG. 19 is a cross sectional view of a heated mattress overlay or padwith partial thickness cuts or channels in the foam layer in accordancewith embodiments of the invention.

FIG. 20 is a perspective view of a heated pediatric mattress overlay orpad in accordance with embodiments of the invention.

FIG. 21 is a cross sectional view of a heated pediatric mattress overlayor pad in accordance with embodiments of the invention.

FIG. 22A-D is a cross sectional view of a heated pediatric mattressoverlay or pad in accordance with embodiments of the invention.

FIG. 23 is a cross sectional view of a heated mattress overlay or padwith a power entry assembly located in the peripheral bond between theshell layers in accordance with embodiments of the invention.

FIG. 24 is an illustration of a heated mattress overlay or pad withattachment tabs in accordance with embodiments of the invention.

FIG. 25 is a cross sectional view of a heated mattress including avisco-elastic foam layer in accordance with embodiments of theinvention.

DETAILED DESCRIPTION

The following detailed description is exemplary in nature and is notintended to limit the scope, applicability, or configuration of theinvention in any way. Rather, the following description providespractical illustrations for implementing exemplary embodiments of thepresent invention. Examples of constructions, materials, dimensions, andmanufacturing processes are provided for selected elements, and allother elements employ that which is known to those of skill in the fieldof the invention. Those skilled in the art will recognize that many ofthe examples provided have suitable alternatives that can be utilized.The term ‘blanket’, used to describe embodiments of the presentinvention, may be considered to encompass heating blankets and pads, andvice-versa. Pads may also be referred to as underbody support systems ormattresses. In other words, features of the invention are applicable toboth blankets and pads, regardless of whether a feature is described ina particular embodiment with regard to a blanket or a pad (e.g.,including mattress overlays and underbody supports).

FIG. 1 shows a heating blanket or pad 100 according to some embodimentsof the present invention. As shown, the heating blanket or pad 100 isgenerally rectangular. Embodiments of the present invention can be usedin connection with a wide variety of heating blankets and pads. Forexample, in some cases, the heating blanket or pad 100 may be a blanketsized and shaped for the upper body or upper body limb (e.g., awrap-around blanket), or a blanket sized and shaped for the lower bodyor lower body limb. In some cases the heating blanket or pad 100 can beused in conjunction with a disposable cover. In other embodiments, theheating blanket or pad 100 may be a mattress overlay or underbodysupport mattress.

The heating blanket or pad 100 of FIG. 1 includes a shell 105 that canbe durable and waterproof. As shown, a portion of the shell 105 is cutaway, revealing a heating element assembly 350. The heating elementassembly 350 is generally covered by the shell 105 and can extend withinthe shell 105 between edge 112 and edge 114 and between edge 116 andedge 118. An electrical connector housing 325 and a correspondingconnector plug 323 can be coupled to the shell 105, thereby enablingaccess to a temperature sensor assembly such as those discussed below.

The shell 105 can protect and isolate the heating element assembly 350from an external environment of heating blanket 100. The shell 105 caninclude a water-resistant material layer that can form a substantiallyhermetic seal around the heating element assembly 350. The shell 105 canprovide further protection to a patient disposed beneath heating blanketor pad 100 against electrical shock hazards. According to preferredembodiments of the present invention, shell 105 is waterproof to preventfluids (e.g., bodily fluids, IV fluids, cleaning fluids, etc.) fromcontacting the heating element assembly 350. In some preferredembodiments, shell 105 may further include an anti-microbial element(e.g., a SILVERion™ antimicrobial fabric available from Domestic FabricsCorporation or Ultra-Fresh™ from Thomson Research Associates).

According to an illustrative embodiment of the present invention, shell105 comprises a nylon fabric having an overlay of polyurethane coatingto provide waterproofing. The coating can be on at least an innersurface of each of two sheets of the shell, further facilitating a heatseal between the two sheets, according to preferred embodiments. Inother embodiments, the shell 105 comprises polyvinyl chloride (PVC) tofacilitate an RF weld to bond the sheets. It should be noted that,according to some embodiments of the present invention, a covering forheating element assemblies may be removable and, thus, include areversible closure facilitating removal of a heating element assembly350 therefrom and insertion of the same or another heating elementassembly 350 therein. In some embodiments, shell 105 comprises a PVCfilm of sufficient thickness to provide the necessary strength. In somesuch embodiments, the edge seals can be softer.

In some embodiments, one or more layers may be positioned between theheating element assembly 350 and the shell 105. For example, in someembodiments, [a layer of thermally insulating material] (e.g., polymericfoam or high-loft fibrous non-woven material) can be included in one ormore locations. In some instances, a layer of thermally insulatingmaterial can be positioned to protect a portion of the patient from theheating element assembly 350 in the event that part of the shell 105 isinadvertently placed under that portion of the patient. In suchinstances, a layer of thermal insulating material can be positionedbetween the heating element assembly 350 and the patient-contactingsurface of the shell 105. In this way, in the event that part of theshell 105 is inadvertently placed under that portion of the patient,that portion of the patient can contact an insulated portion of theshell 105 rather than a non-insulated portion of the shell 105.

In some instances a layer of thermally insulating material can bepositioned to make sure that a maximal amount of heat being generated bythe heating element assembly 350 is transferred to the patient. In suchinstances, a layer of thermally insulating material can help insulatethe heating element assembly 350 from the environment and provide a moreuniform temperature distribution. The layer of thermally insulatingmaterial can be positioned between the heating element assembly 350 andthe surface of the shell 105 that does not contact the patient. In thisway, a maximal amount of heat being generated by the heating elementassembly 350 can be transferred to the patient and not to thesurrounding environment.

In some instances a layer of thermally insulating material can bepositioned to prevent caregivers from experiencing unwanted contact withactivated heating blankets or pads. Other layers (e.g., an electricallyinsulating layer similar to those discussed elsewhere herein) can bepositioned between the heating element assembly 350 and the shell 105.

FIGS. 2A-2B show an illustrative heating blanket or pad subassembly 300that can be incorporated into heating element assemblies in someembodiments of the present invention (e.g., heating element assembly 350of FIG. 1 ). Referring again to FIGS. 2A-2B, in many embodiments, theheating blanket or pad subassembly 300 is flexible. The heating blanketor pad subassembly 300 can include a flexible sheet-like heating element310, or heater, which can include a first side edge 301 and a secondside edge 302. According to preferred embodiments of the presentinvention, heating element 310 comprises a conductive fabric or a fabricincorporating closely spaced conductive elements such that heatingelement 310 has a substantially uniform watt density output, preferablyless than approximately 0.5 watts/sq. inch, and more preferably betweenapproximately 0.2 and approximately 0.4 watts/sq. inch, across a surfacearea, of one or both sides 313, 314 (FIG. 2B).

Some examples of conductive fabrics which may be employed by embodimentsof the present invention include, without limitation, carbon fiberfabrics, fabrics made from carbonized fibers, conductive films, or wovenor non-woven non-conductive fabric or film substrates coated with aconductive material, for example, polypyrrole, carbonized ink, ormetalized ink. In many embodiments, the conductive fabric is a polymericfabric coated with a conductive polymeric material such as polypyrrole.In addition, the flexible heating element 310 may be made from a matrixof electrically resistant wire or metal traces attached to a fibrous orfilm material layer.

In some embodiments, in contrast to non-stretchable conductive filmheaters, where a carbon (or other conductive material) impregnatedplastic film is extruded onto or bonded onto a base layer such as afabric base layer, the preferred heating element 310 material has aconductive or semi-conductive material coated onto the individualthreads or fibers of the carrier fibers prior to weaving or knittinginto a fabric. This maintains the natural flexibility andstretch-ability of the fabric rather than turning the fabric into anon-stretchable fiber reinforced film.

In some embodiments, the conductive or semi-conductive coating comprisesa polymer and is bound as a layer surrounding the individual threads orfibers by a process of polymerization. Polymerization results in a verysecure bond. The flexible coating on each individual thread or fiberpreferably does not crack, fracture or delaminate during flexion.Polymerization of these conductive or semi-conductive materials ontoindividual fibers of the carrier fabric is a preferable process forproducing a durable, flexible and stretchable heater assembly 300.Semi-conductive polymer coatings such as polypyrrole are preferred forthis invention, however, other coating processes are anticipated andconductive coatings that use carbon or metal as the conductive materialare also anticipated

In some embodiments, the conductive material may be stretchable in atleast one direction or, alternatively, in at least two directions. Oneway to create a stretchable fabric heating element (e.g., 310) is tocoat a conductive material onto individual threads or fibers of acarrier fabric which may be a non-conductive material. The threads orfibers may be woven or knitted, for example, into a stretchable fabric.Other examples of conductive fabrics which may be employed include,without limitation, carbon fiber fabrics, fabrics made from carbonizedfibers, and woven or non-woven substrates coated with a conductivematerial, for example, polypyrrole, carbonized ink, or metalized ink.

The conductive material may be applied to the fibers or threads beforethey are woven or knit into a fabric. In this way, the coated threadscan move and slide relative to each other as the fabric is stretched,and can return to their original orientation when the stretching isstopped such that the fabric can return to its original shape.Alternatively, the conductive materials that coat the individual fibersin the fabric may be applied after the fabric is woven or knit using adipping, spraying, coating or polymerization process or combinationsthereof. A conductive polymer can be selected that coats to theindividual threads without bonding them together such that the threadsremain able to slide relative to each other.

The stretchable fabric heating element (e.g., 310) is able to deform inresponse to a focal pressure applied to the surface of the heaterfabric, into a smooth 3-dimensional compound curve without wrinkling orfolding. A smooth compound curve cannot be formed out of non-stretchablefabrics or films. The stretchable fabric heating element may alsoexhibit elastic properties that allow it to revert to its originalplanar shape when the deforming pressure is relieved. The fabric heatingelement can be provided with appropriate tensile properties such thatthe amount of stretch, or strain, required to prevent hammocking andallow accommodation of the patient into the heated mattress or mattressoverlay does not result in stresses that exceed the elastic limit of thematerial. In some embodiments, for example, an increase in the width ofa 20 inch wide mattress or mattress overlay of approximately one inchduring stretching achieves the desired goals without exceeding theelastic limit of the stretchable fabric heating element or introducingpermanent plastic deformation.

FIG. 2A further illustrates subassembly 300 including two bus bars 315coupled to heating element 310 for powering heating element 310. Eachbus bar 315 is shown extending between first and second side edges 301,302. With reference to FIG. 2B, according to some embodiments, bus bars315 are coupled to heating element 310 by a stitched coupling 345 (e.g.,formed with conductive thread such as silver-coated polyester or nylonthread (Marktek Inc., Chesterfield, Mo.)).

As shown, insulation is provided between the bus bars 315 and theheating element 310. FIG. 2B illustrates subassembly 300 whereininsulating members 318 (e.g., fiberglass material strips having anoptional PTFE coating and a thickness of approximately 0.003 inch)extend between bus bars 315 and heating element 310 at each stitchedcoupling 345, so that electrical contact points between bars 315 andheating element 310 are solely defined by the conductive thread ofstitched couplings 345. Alternatively, the electrical insulationmaterial layer could be made of polymeric film, a polymeric filmreinforced with a fibrous material, a cellulose material, a glassfibrous material, rubber sheeting, polymeric or rubber coated fabric orwoven materials or any other suitable electrically insulating material.

Each of the conductive thread stitches of coupling 345 can maintain astable and constant contact with bus bar 315 on one side and heatingelement 310 on the other side of insulating member 318. The stitchesproduce a stable contact in the face of any degree of flexion, so thatthe potential problem of intermittent contact between bus bar 315 andheating element 310 (that could arise for the embodiment shown in FIG.2B, where bus bar 315 is in physical contact with heating element 310)can be avoided. The stitches (e.g., 345) are the only electricalconnection between bus bar 315 and heating element 310, but, since theconductive thread has a much lower electrical resistance than theconductive fabric of heating element 310, the thread does not heat undernormal conditions.

In addition to heating blanket applications described herein, such adesign for providing for a uniform and stable conductive interfacebetween a bus bar and a conductive fabric heating element material canbe used in other applications. For example, such a design can improvethe conductive interface between a bus bar or electrode and a conductivefabric in non-flexible heating elements, in electronic shielding, inradar shielding and other applications of conductive fabrics.

In some preferred embodiments, coupling 345 includes two or more rows ofstitches for added security and stability. However, due to the flexiblenature of blanket or pad subassembly 300, the thread of stitchedcouplings 345 may undergo significant stresses. These stresses, overtime and with multiple uses of a blanket or pad containing subassembly300, could lead to one or more fractures along the length of stitchedcoupling 345. Such a fracture, in other designs, could also result inintermittent contact points, between bus bar 315 and heating element 310that could lead to a thermal breakdown of heating element 310 along busbar 315. But, if such a fracture were to occur in the embodiment of FIG.2B, insulating member 318 may prevent a thermal breakdown of heatingelement 310, so that only the conductive thread of stitched coupling 345melts down along bus bar 315. According to some preferred embodiments,more than two rows of stitches are applied to each bus bar 315 for addedsafety and stability of the bus bar 315/heating element 310 interface.

Alternative threads or yarns employed by embodiments of the presentinvention may be made of other polymeric or natural fibers coated withother electrically conductive materials. In addition, nickel, gold,platinum and various conductive polymers can be used to make conductivethreads. Metal threads such as stainless steel, copper or nickel couldalso be used for this application.

According to an exemplary embodiment, bus bars 315 are comprised offlattened tubes of braided wires, such as are known to those skilled inthe art (e.g., a flat braided silver coated copper wire) and may thusaccommodate the thread extending therethrough, passing through openingsbetween the braided wires thereof. In addition such bus bars 315 areflexible to enhance the flexibility of blanket or pad subassembly 300.According to alternate embodiments, bus bars 315 can be a conductivefoil or wire, flattened braided wires not formed in tubes, an embroideryof conductive thread, or a printing of conductive ink. Preferably, busbars 315 are each a flat braided silver-coated copper wire material,since a silver coating has shown superior durability with repeatedflexion, as compared to tin-coated wire, for example, and may be lesssusceptible to oxidative interaction with a polypyrrole coating ofheating element 310 according to an embodiment described below.Additionally, an oxidative potential, related to dissimilar metals incontact with one another is reduced if a silver-coated thread is usedfor stitched coupling 345 of a silver-coated bus bar 315.

According to an exemplary embodiment, a conductive fabric comprisingheating element 310 comprises a non-woven polyester having a basisweight of approximately 170 g/m2 and being 100% coated with polypyrrole(available from Eeonyx Inc., Pinole, Calif.). The coated fabric has anaverage resistance (e.g., determined with a four point probemeasurement) of approximately 15 ohms per square inch. This averageresistance is suitable to produce the preferred watt density of 0.2 to0.4 watts/sq. in. for surface areas of heating element 310 having awidth, between bus bars 315, in the neighborhood of about 19 to 28inches, when powered at about 48 volts. In some embodiments, the basisweight of the non-woven polyester may be chosen in the range ofapproximately 80-180 g/m2. However, other basis weights may beengineered to operate adequately are therefore within the scope ofembodiments of the invention.

A resistance of such a conductive fabric may be tailored for differentwidths between bus bars 315 (wider requiring a lower resistance andnarrower requiring a higher resistance) by increasing or decreasing asurface area of the fabric that can receive the conductive coating. Insome instances, this can be achieved by increasing or decreasing thebasis weight of the nonwoven. Resistance over the surface area of theconductive fabrics (e.g., 310) is generally uniform in many embodimentsof the present invention. However, the resistance over differentportions of the surface area of conductive fabrics such as these mayvary (e.g., due to (a) variation in a thickness of a conductive coating,(b) variation within the conductive coating itself, (c) variation ineffective surface area of the substrate which is available to receivethe conductive coating, or (d) variation in the density of the substrateitself). Local surface resistance across a heating element, for exampleheating element 310, is directly related to heat generation according tothe following relationship:Q (Joules)=I2 (Amps)×R (Ohms)

Variability in resistance thus translates into variability in heatgeneration, which can ultimately manifest as a variation in temperature.

According to preferred embodiments of the present invention, which areemployed to warm patients undergoing surgery, precise temperaturecontrol is desirable. Means for determining heating element 310temperatures, which average out temperature variability caused byresistance variability across a surface of the heating element 310, aredescribed below in conjunction with FIG. 3A.

Referring again to FIGS. 2A-2B, the flexibility of blanket or padsubassembly 300 can allow blanket or pad subassembly 300 to conform tothe contours of a body (e.g., all or a portion of a patient undergoingsurgery). This flexibility can be provided primarily by flexible heatingelement 310 and can be optionally enhanced by the incorporation offlexible bus bars 315. Conforming to the contours of a patient's body ispreferable to simply bridging across high spots of the body. Suchconformance may optimize a conductive heat transfer from heating element310 to a surface of the body.

The uniform watt-density output across the surface areas of preferredembodiments of heating element 310 translates into generally uniformheating of the surface areas, but not necessarily a uniform temperature.For example, at locations of heating element 310 which are in conductivecontact with a body acting as a heat sink, the heat is efficiently drawnaway from heating element 310 and into the body (e.g., by blood flow).At the same time, at those locations where heating element 310 does notcome into conductive contact with the patient's body, an insulating airgap exists between the body and those portions, so that the heat is notdrawn off those portions as easily. Therefore, those portions of heatingelement 310 not in conductive contact with the body will gain intemperature, since heat is not transferred as efficiently from theseportions as from those in conductive contact with the body. The‘non-contacting’ portions will reach a higher equilibrium temperaturethan that of the ‘contacting’ portions, when the radiant and convectiveheat loss equal the constant heat production through heating element310. Since the heat generation is generally uniform, the heat flux tothe patient will also be generally uniform. However, at thenon-contacting locations, the temperature is higher to achieve the sameflux as the contacting portions. Some of the extra heat from the highertemperatures at the non-contacting portions can therefore be dissipatedout the back of the blanket or pad 100 instead of into the patient.

Although radiant and convective heat transfer are more efficient athigher heater temperatures, the laws of thermodynamics dictate that aslong as there is a uniform watt-density of heat production, even at thehigher temperature, the radiant and convective heat transfer from ablanket or pad of this construction will result in a generally uniformheat flux from the blanket or pad. Therefore, by controlling the‘contacting’ portions to a safe temperature (e.g., via a temperaturesensor assembly 321 coupled to heating element 310 in a location whereheating element 310 will be in conductive contact with the body), the‘non-contacting’ portions, will also be operating at a safe temperaturebecause of the less efficient radiant and convective heat transfer.

According to preferred embodiments, heating element 310 comprises aconductive fabric having a relatively small thermal mass. When a portionof such a heating element that is operating at the higher temperature istouched, suddenly converting a ‘non-contacting’ portion into a‘contacting’ portion, that portion will cool almost instantly to thelower operating temperature.

FIGS. 3A-3B show a heating element assembly 350 similar to the heatingelement assembly 350 of FIG. 1 . Referring again to FIGS. 3A-3B, theheating element assembly 350 can include a temperature sensor assembly321. As shown, the temperature sensor assembly 321 is coupled to heatingelement 310 at a location where heating element 310 would come intoconductive contact with the patient. This can assist in maintaining asafe temperature distribution across heating element 310. The moreconstant the temperature information, the more the temperaturecontroller can rely on it in controlling the heater (e.g., heatingelement 310, heating element assembly 350) temperature. In someembodiments, the temperature sensor assembly 321 can even be providedseparately from the heating blanket or pad.

According to embodiments of the present invention, zones of heatingelement 310 may be differentiated according to whether or not portionsof heating element 310 are in conductive contact with a body (e.g., apatient undergoing surgery). In some embodiments, the thresholdtemperature is between 37 and 43° C. In one particular embodiment, thethreshold temperature is 43° C. A temperature of 43° C. has been shownto provide beneficial warming to a patient without providing excessiveheat. In the case of conductive heating, gentle external pressure may beapplied to a heating blanket or pad 100 including heating element 310.Such pressure conforms heating element 310 into better conductivecontact with the patient to improve heat transfer. However, if excessivepressure is applied, the blood flow to that skin may be reduced at thesame time that the heat transfer is improved and this combination ofheat and pressure to the skin can be dangerous. It is well known thatpatients with poor perfusion should not have prolonged contact withtemperatures in excess of approximately 42° C. Several studies show 42°C. to be the highest skin temperature that cannot cause thermal damageto normally perfused skin, even with prolonged exposure. (Stoll &Greene, Relationship Between Pain and Tissue Damage Due to ThermalRadiation. J. Applied Physiology 14(3):373-382. 1959; and Moritz andHenriques, Studies of Thermal Injury: The Relative Importance of Timeand Surface Temperature in the Causation of Cutaneous Burns. Am. J.Pathology 23:695-720, 1947). Thus, according to certain embodiments ofthe present invention, the portion of heating element 310 that is inconductive contact with the patient is controlled to approximately 43°C. in order to achieve a temperature of about 41-42° C. on a surface ofa heating blanket or pad cover (e.g., shell 105 of FIG. 1 ) thatsurrounds heating element 310.

FIG. 3B illustrates the temperature sensor assembly 321 assembled onside 314 of the heating element 310. As shown, the heating element 310is overlaid on both sides 313, 314 with an electrically insulating layer330. The electrically insulating layer 330 is preferably formed of aflexible non-woven very low loft fibrous material (e.g., 1.5ounces-per-square-yard nylon), which is preferably laminated to sides313, 314 with a hotmelt laminating adhesive. In some embodiments, theadhesive is applied over the entire interfaces between insulating layer330 and heating element 310. Other examples of suitable materials forinsulating layer 330 include, without limitation, polymeric foam, awoven fabric, such as cotton or fiberglass, and a relatively thinplastic film, cotton, and a non-flammable material, such as fiberglassor treated cotton. According to preferred embodiments, overlaidinsulating layers 330 prevent electrical shorting of one portion ofheating element 310 with another portion of heating element 310 if theheating element 310 is folded over onto itself. Many such embodimentsprevent electrical shorting without compromising the flexibility ofheating assembly 350. Heating element assembly 350 may be powered by arelatively low voltage (approximately 48V). Insulating layers 330 mayeven be porous in nature to further maintain the desired flexibility ofassembly 350.

As shown in FIG. 3A, an assembly of leads 305, 306 and junctions 355 canconnect the bus bars 315 and the temperature sensor assembly 321 to anelectrical connector housing 325. Leads 305 couple the connector housing325 to bus bars 315 at junctions 355. Lead 306 couples the temperaturesensor assembly 321 to the connector housing 325. In many embodiments,leads 305, 306 extend over any insulating layer (e.g., 330 in FIG. 3B)and into the electrical connector housing 325. As is noted above (seediscussion in connection with FIG. 1 ) and discussed in greater detailbelow (see discussion in connection with FIG. 4A), electrical connectorhousing 325 can contain a connector plug 323.

Returning now to FIG. 3B, the illustrative temperature sensor assembly321 will be described in greater detail. The temperature sensor assembly321 can include a temperature sensor 351 (e.g., a surface mount chipthermistor (such as a Panasonic ERT-J1VG103FA: 10K, 1% chip thermistor))soldered to an etched metal foil. In many embodiments, a substrate 331(e.g., of polyimide (Kapton)) surrounds the temperature sensor 351. Aheat spreader 332 (e.g., a copper or aluminum foil) can be mounted to anopposite side of substrate 331 (e.g., being bonded with a pressuresensitive adhesive). Substrate 331 can be relatively thin (e.g., about0.0005-inch thick) so that heat transfer between heat spreader 332 andsensor is not significantly impeded.

In some embodiments, the temperature sensor 351 is positioned such thatthe regions surrounding sensor 351 will be in conductive contact withthe body when a heating blanket or pad is placed over a body. Aspreviously described, in many instances, it is desirable that atemperature of approximately 43° C. be maintained over a surface ofheating element 310 which is in conductive contact with a body of apatient undergoing surgery. An additional alternate embodiment iscontemplated in which an array of temperature sensors are positionedover the surface of heating element 310, being spaced apart to collecttemperature readings. In some such embodiments, the collectedtemperatures can be averaged to account for resistance variance.

FIGS. 4A-4B show a heating element assembly 350 that may be incorporatedinto a heating blanket or pad (e.g., heating blanket or pad 100 of FIG.1 ). As shown, the heating element assembly 350 includes heating element310 overlaid with electrical insulation 330 on both sides 313, 314 and athermal insulation layer 311 extending over the top side 314 thereof(dashed lines show leads and sensor assembly beneath layer 311).

A heating blanket or pad may 100 include a layer of thermal insulation311 extending over a top side (corresponding to side 314 of heatingelement 310 as shown in FIG. 2B) of heating assembly 350 as discussedabove. According to the illustrated embodiment, layer 311 is insertedbeneath a portion of each insulating member 318. The insulating members318 have been folded over the respective bus bar 315 (e.g., asillustrated by arrow B in FIG. 2B), and then held in place by arespective row of non-conductive stitching 347 that extends throughinsulating member 318, layer 311 and heating element 310. Although notshown, it should be appreciated that layer 311 may further extend overbus bars 315. Although insulating layer 330 is shown extending beneathlayer 311 on side 314 of heating element 310, according to alternateembodiments, layer 311 independently performs as a thermal andelectrical insulation so that insulating layer 330 is not required onside 314 of heating element 310. FIG. 4A further illustrates, withlongitudinally extending dashed lines, a plurality of optional slits 303in layer 311, which may extend partially or completely through layer311, in order to increase the flexibility of assembly 350. Such slits303 are desirable if a thickness or density of layer 311 is such that itprevents the heating blanket or pad 100 from draping (e.g., curving,deforming) effectively about a patient. The optional slits 303 arepreferably formed, for example, extending only partially through layer311 starting from an upper surface thereof, to allow bending of theheating blanket or pad 100 about a patient and to prevent bending of theheating blanket or pad 100 in the opposition direction.

Returning now to FIG. 3A, to be referenced in conjunction with FIGS. 1and 4A, connector housing 325 and connector plug 323 will be describedin greater detail. According to certain embodiments, housing 325 is aninjection molded thermoplastic (e.g., PVC) and may be coupled toassembly 350 by being stitched into place, over insulating layer 330.FIG. 3A shows housing 325 including a flange 353 through which suchstitching can extend.

Referring to FIGS. 1 and 4A, in some embodiments, a surface of flange353 of housing 325 protrudes through a hole formed in thermal insulatinglayer 311 so that a seal may be formed (e.g., by adhesive bonding and/orwelding, such as heat sealing) between an inner surface of shell 105 andsurface 352. According to one embodiment, wherein housing 325 isinjection molded PVC and the inner surface of shell 105 is likewise PVC,housing 325 is sealed to shell 105 via a solvent bond. It may beappreciated that the location of the connector plug 323 is suitable tokeep the corresponding connector cord well away from the surgical field.In embodiments in which the inner surface of shell 105 is coated withpolyurethane and the housing 325 is injection molded PVC, anintermediate adhesive can be used to allow for a heat seal connection(e.g., a solvent bond adhesive can be applied to the housing 325, andthe polyurethane film can be heat sealed to the exposed adhesive).

FIGS. 4A-4B further illustrate a pair of securing strips 317, eachextending laterally from and alongside respective lateral portions ofheating element 310, parallel to bus bars 315, and each coupled to side313 of heating element 310 by the respective row of non-conductivestitching 347. Another pair of securing strips 371 is shown in FIG. 4A,each strip 371 extending longitudinally from and alongside respectiveside edges 301, 302 of heating element 310 and being coupled thereto bya respective row of non-conductive stitching 354. Strips 371 may extendover layer 311 or beneath heating element 310. As shown, strips 317preferably extend over conductive stitching of stitched coupling 345 onside 313 of heating element 310. The strips 317 can provide a layer ofinsulation that can prevent shorting between portions of side 313 ofheating element 310 if heating element 310 were to fold over on itselfalong rows of conductive stitching of stitched coupling 345 that couplebus bars 315 to heating element 310. In some embodiments, strips 317 mayalternately extend over insulating member 318 on the opposite side ofheating element 310. According to the illustrated embodiment, securingstrips 317 and 371 are made of a polymer material (e.g., PVC). They maybe heat sealed between the sheets of shell (105 of FIG. 1 ) incorresponding areas of the heat seal zone in order to secure heatingelement assembly 350 within a corresponding gap between the two sheetsof shell (105 of FIG. 1 ). According to an alternate embodiment, forexample, shown by dashed lines in FIGS. 2A and 4B, heating element 310extends laterally out from each bus bar 315 to a securing edge 327,which may include one or more slots or holes 307 extending therethroughso that inner surfaces of sheets of shell (105 of FIG. 1 ) can contactone another to be sealed together and thereby hold edges 327.

Referring to FIG. 1 , connector plug 323 can protrude from shell 105 ofthe heating blanket 100. An extension cable (e.g., FIG. 1 ) may couplethe heating element assembly 350 to a console 60. The console 60includes a shut-off timer 30 and a power source 50 each coupled to acontrol system (e.g., controller) 41. The shut-off timer 30 can beoperatively coupled to the control system 41, meaning that the shut-offtimer 30 can be integrated into the control system 41, the shut-offtimer 30 can be a separate component, or the shut-off timer 30 and thecontrol system 41 can have any other suitable functional relationship.The temperature sensor assembly 321 can be configured to providetemperature information to the control system 41, which may act as atemperature controller. The controller may function to interrupt suchpower supply (e.g., in an over-temperature condition) or to modify theduty cycle to control the heating element temperature.

The power source 50 and power type can be any type known in the art. Incertain embodiments, the power source 50 supplies a straight-line DCvoltage to the control system 41, and the control system 41 provides apulse-width-modulated voltage (e.g., at a 75% duty cycle) to the heatingelement assembly 350. Of course, other duty cycles and/or voltage levelscan be used based on the design of the blanket or pad 100 and itsheating element in order to achieve a desired threshold temperature in areasonable amount of time. Too high of voltage or duty cycle, whiledecreasing the time to reach the desired temperature threshold, mayincrease the amount of temperature overshoot before the control system41 reduces or shuts off power. Moreover, in the case of temperaturesensor (e.g., 321) failure, thermal runaway presents a greater concernwith relatively higher voltage or duty cycle settings. Too low of avoltage or duty cycle may cause unreasonably long warm-up times.

As discussed above, warming blankets and pads in accordance withembodiments of the invention include or make use of a shell or covering,such as shell 105 shown in FIG. 1 . Several embodiments of such shellswill now be described in greater detail, although it should beunderstood that these embodiments are for illustrative purposes only.

FIG. 5A is a cross-section of a shell 500 containing a heating element502 in accordance with some embodiments of the invention. The shell 500can include a top sheet 504 and a bottom sheet 506 that are welded orcoupled at one or more locations in order to define a pocket or pouch508 that can enclose the heating element 502. Heating element 502 mayinclude characteristics of heating element 310 or may be included in aheating element assembly such as 350. Any type of suitable weld may beused, such as heat welding (heat bonding), RF welding, ultrasonicwelding, etc., depending on the type of materials used in sheets 504,506. Each sheet 504 and 506 can comprise a flexible, substantiallywater-resistant material and include the ability to be welded together.As one of ordinary skill in the art would consider, sheets 504, 506 maybe formed of two or more distinct sheets of material, including a singlesheet of material folded over on itself or any other suitableconstruction. In some embodiments, the water-resistant material includesa single layer, and in some embodiments, the sheets 504, 506 arecomprised of a laminate of two or more layers. For instance, in someembodiments one or both of sheets 504, 506 are comprised of a singlelayer of polyvinyl chloride (PVC). In such embodiments where PVC isused, high frequency or RF welding (RF heat sealing) may be used to bondthe sheets 504, 506 together. PVC sheets also provide a water-resistantmaterial in order to protect the heating element 502 from fluids towhich the heating blanket or pad 100 is exposed.

In some embodiments, one or both of sheets 504, 506 include respectivestrengthening layers 510, 512 that provide strength and color to theshell 500. For example, the strengthening layers 510, 512 can be afibrous material such as woven nylon. It will be appreciated that othermaterials can also be used for this layer.

With further reference to FIG. 5A, sheets 504, 506 can each also includea second layer 514, 516 located along an inside surface of the sheets504, 506. These second layers 514, 516 may in some embodiments provide awater-resistant layer in order to protect the heating element 502 fromfluids to which the heating blanket or pad is exposed. For example, thesecond layers 514, 516 may be a polymeric film attached to thestrengthening layer. In some embodiments, the second layers 514, 516 arepreferably polymeric film layers that are a durable and made of aweldable material, such as urethane or vinyl, which can be laminated orextrusion coated on to the strengthening layers 510, 512 and the secondlayers 514, 516 may be welded together via heating bonding along thebonding points.

In some embodiments, one or both of sheets 504, 506 include a thirdlayer laminated to their respective outer surfaces. The third layer, insome embodiments, is a polymeric layer, which may or may not be the samematerial as second layers 514, 516 in some embodiments. For example, thethird layer may comprise a polymeric layer that can substantially sealone or both of the strengthening layers so that it cannot besubstantially wetted. In some embodiments, the third layer may also besomewhat tacky so that it prevents the blanket from slipping whenapplied over a patient, or a patient from slipping when provided on apad. The third layer may also comprise a material with the ability tolimit and/or prevent iodine and cleaning solutions from staining theblanket or pad. Examples of materials that could serve this purposeinclude vinyl and silicone.

With further reference to FIG. 5A, top sheet 504 (e.g., first sheet) andbottom sheet 506 (e.g., bottom sheet) can be positioned on opposingsides of heating element 502 to envelope the heating element. Althoughdescriptive terms “top” and “bottom” are used herein, it will beappreciated that in some embodiments, the sheets 504 and 506 may beidentical and that either sheet may be referred to as “top” or “bottom”,or “first” and second. Sheets 504 and 506 may be formed of a singularpiece of material folded over on itself to provide the two sheets, or atleast two sheets. Although sometimes referred to as a first sheet 504and second sheet 506, the first and second sheets 504, 506 may be formedof a singular piece of material folded over on itself to provide thefirst sheet 504 and the second sheet 506. As shown in the embodiment ofFIG. 5A, the sheets 504, 506 are positioned so that the weldable layers514, 516 of each sheet oppose each other.

FIG. 5B is a top plan view of the heating blanket or pad 500 depicted inFIG. 5A. In some embodiments, the sheets 504, 506 are sized tocompletely cover the heating element 502, and can extend beyond alledges (e.g., top, bottom, right and left side edges in FIG. 5B) of theheating element 502. In some embodiments, the heating element 502 issubstantially hermetically sealed into the shell 500 formed by the twosheets 504, 506 (e.g., two or more distinct sheets or one sheet foldedover on itself to form two sheets). As shown in the embodiment of FIGS.5A and 5B, the sheets 504, 506 are coupled together along two welds. Afirst weld 518 can extend about a perimeter 520 of the heating element502, thus surrounding the entire periphery of the heating element 502. Asecond weld 522 can extend about a perimeter edge 524 of the sheets 504,506, thus sealing the periphery of the sheets 504, 506 together. In someembodiments, a space 526 between the first weld 518 and the second weld522 may be totally or partially welded together. In alternateembodiments, the space 526 between the welds 518, 520 may contain otherstructural components of the blanket or pad as previously described andfurther discussed below. For example, the space 526 can encloseweighting members, the added weight of which helps retain the blanket orpad in position and against the patient.

The weld(s) used in some embodiments to create a substantiallyhermetically sealed shell (e.g., 105; 504, 506) for protecting theheating element (e.g., 310, 502) provides a number of advantages overtraditional bonding mechanisms such as sewing, stitches, rivets orgrommets that create or reinforce a seal. In certain embodiments ofthose that employ a heat sealed shell, the external surface of thesubstantially hermetically sealed shell is not punctured by needleholes, sewing, stitching, rivets, grommets or other fasteners. Thesetraditional fasteners create holes and can accumulate contaminants fromblood and body fluids. These holes, crevasses, and fibrous materialssuch as thread are difficult or even impossible to clean with standardcleaning methods and solutions. Exemplary heating blankets and padsdescribed herein can advantageously have a smooth, non-violated shell,without external attachments or physical places to trap contaminants,thus providing a readily and thoroughly cleanable heating blanket or padin some embodiments. As will be appreciated, the welded constructionused in some embodiments can also facilitate a variety of features thatwould otherwise require traditional fasteners such as sewing, stitching,riveting, grommets or snaps.

In some embodiments, portions of the shell extending beyond theperimeter of the heating element can form non-heated edge flaps of theheating blanket or pad, such as those described above. Exemplarynon-heated edge flaps can preferably extend from 1 inch to 24 inchesaway from the perimeter of the heating element, although it will beappreciated that any suitable length of extension is possible. Thenon-heated edge flaps can be used to create a cocoon-like space thattraps the heat from the heater in a space around the patient. Forexample, in alternative embodiments, the edges 112, 114, 116, and 118 ofthe heating blanket or pad 100 depicted in FIG. 1 can include non-heatededge flaps instead of lateral portions of the heating element 310. Thenon-heated edge flaps can thus create a thermal barrier between theheater edge and the operating table or bed. In some embodiments, the twosheets of the non-heated edge flaps may be partially or completelywelded together between the first weld about the perimeter of theheating element and the second weld about the perimeter of the warmingblanket or pad. With reference to FIG. 6 , in embodiments with a partialweld, the non-welded area may include an air pocket 530. Air can beintroduced into the space 526 between the first weld 518 and the secondweld 522. Embodiments with such an air pocket 530 can thus provide athermal barrier that further limits the escape of heat from the spacearound the patient.

With reference to FIG. 7A, some exemplary heating blankets and pads caninclude one or more straps 532 extending from the blanket or pad forsecuring the blanket in place over the patient or the pad in place underthe patient. In some embodiments, the straps 532 are preferably of thesame material and contiguous with the sheets 504, 506 making up theshell 500 and protrude from the edges of the sheets 504, 506 such thatthere is no seam joining the straps 532 with the sheets 504, 506. Insome embodiments, holes 534 can be punched in the straps 532 tofacilitate buckling the straps (e.g., to another blanket strap extendingfrom a different edge of the blanket, to a protuberance extending fromthe blanket, etc.), hanging the warming blanket, or other common uses.With reference to FIG. 7B, some embodiments can include a reinforcinglayer 536 positioned between the sheets 504, 506 before they are weldedin order to reinforce the straps 532. For example, the reinforcing layer536 can in some embodiments comprise a plastic film such as a urethanefilm. The reinforcing layer 536 may be formed in addition tostrengthening layer of sheets 504, 506 described above. Alternatively,the reinforcing layer 536 could be formed by the inclusion of thestrengthening layer 510, 512 on one or both of sheets 504, 506 at thestrap locations shown in FIG. 7A. As will be appreciated, the straps 532are provided with the warming blanket or pad without the addition ofsewing, stitching, grommets or other traditional fasteners, thusproviding the advantages previously discussed.

As previously discussed with reference to at least FIGS. 2A, 4A and 4B,securing strips 317, 371 or securing edges 327 can be provided in someembodiments to facilitate securing the heating element (e.g., 310) tothe shell (e.g., 105). With reference to FIG. 8 , an exemplary securingstrip 540 can comprise a weldable plastic film, for example, a urethanefilm. A first end 542 of the securing strip 540 can be attached to theheating element 502, for example by sewing. A second end 544 of thesecuring strip 540 (or securing edge according to alternate embodiments)can be placed between the two sheets 504, 506 and incorporated into thewelds between the two sheets. Thus the heater assembly is held in anextended position within the shell, without using stitches, sewing,rivets or grommets that would pierce the flexible material sheets andmake the shell difficult to clean.

With reference to FIGS. 9A-9B, some exemplary shells 500 providereinforced hanger points 550 without the use of grommets or anothersimilar mechanism for reinforcement. As shown, a reinforcing layer 552extends between the sheets 504, 506 where they are welded at one endabout the perimeter of the heating element 502. The reinforcing layer552 may be formed in addition to strengthening layer of sheets 504, 506.In some embodiments more than one reinforcing layer may be utilized, forexample, on opposing ends of the shell 500 or one layer integrated intoone of both of sheets 504, 506. The reinforcing layer 552 can in someembodiments comprise one or more pieces of thermally bondable plasticfilm, for example a urethane film. The reinforcing layer 552 isincorporated into a weld 554 that may extend from near the perimeter ofthe heating element 502 to near the perimeter of the sheets 504, 506.One or more holes can be punched through both sheets and through thereinforcing layer 552 to create a hanging point 550. The exemplaryreinforcing layer 552 reinforces the hanging point 550 without the needfor additional grommets that would make the blanket or pad moredifficult to clean.

With reference to FIGS. 10A-10B, exemplary shells 500 are shown with anincorporated anchor point 560. As shown, the anchor point 560 can insome embodiments be a “ball-shaped” or a “mushroom-shaped” protuberancewhich can serve as an attachment post on which a strap with holes in itmay be secured, for example, the straps of FIGS. 7A-7B. The anchor point560 can be made of plastic or some other material such as metal. Asshown in FIGS. 10A-10B, the anchor point 560 can be molded or otherwiseattached to an anchoring layer 562, which in some embodiments comprisesa flat piece of thermally bondable plastic material, such as, forexample, a urethane material. The anchoring layer 562 can be placedbetween the two sheets 504, 506 about the perimeter of the heatingelement 502 and the anchor point 560 can extend from the edges of thesheets as in FIG. 10B or through a hole 564 made in one of the sheets asin FIG. 10A. The sheets 504, 506 can be welded to the anchoring layer562 to anchor the anchoring layer 562 between the sheets 504, 506 andalso to seal the cut edge of the hole 564 or edge of the sheets 504,506.

In some embodiments, a piece of ribbing or piping can be molded to theedge of an anchoring layer similar to that shown in FIG. 10B. Theanchoring layer can then be placed between the two sheets at their edgessuch that the ribbing or piping protrudes beyond the edges of thesheets. Exemplary ribbing or piping may be plastic or another suitablematerial such that the ribbing or piping advantageously seals the edgesof the shell and creates a soft edge to the warming blanket or pad.Portions of the ribbing or piping may include the anchor point 560.

With reference to FIG. 11 , in some embodiments, a warming blanket orpad can be secured to a patient, about a patient, or to a surgical tablewith one or more magnets 574 and/or ferrous metal pieces. FIG. 11 showstwo opposing ends 570, 572 of a single shell 500 and warming blanket orpad configured in a loop according to some embodiments. As shown, amagnet 574 can be fixed in position between sheets 504, 506 at end 570via appropriately placed welds of sheets 504, 506. Alternately a ferrousmetal piece 576 or another magnet can be fixed in position betweensheets 506, 504 at end 572 in the same manner as magnet 574. The magnet574 is placed in a position to mate with ferrous metal piece 576,securing the blanket or pad in place. The metal piece 576 and the magnet574 are both contained between the sheets 504, 506 and therefore do notcomplicate the cleaning of the warming blanket or pad.

Embodiments of the heated blanket or pads described herein may beprovided as a pad in the form of a heated underbody support. The termunderbody support may be considered to encompass any surface situatedbelow and in contact with a user in a generally recumbent position, suchas a patient undergoing surgery including heated mattresses, heatedmattress overlays and heated pads. Heated mattress overlay embodimentsmay be identical to heated pad embodiments, with the difference beingwhether or not they are used on top of a mattress. Furthermore, thedifference between heated pad embodiments and heated mattressembodiments may be the amount of support and accommodation they provide,and some pads may be insufficiently supportive to be used alone like amattress. As such, the various aspects which are described herein applyto mattresses, mattress overlays and pad embodiments, even if only onetype of support is shown in the specific example.

Described herein are various embodiments of warming pads that improvepatient warming effectiveness by increasing accommodation of the patientinto the pad, in other words, by increasing the contact area between thepatient's skin and the heated surface of the pad (e.g, heated mattress,mattress overlay). In some embodiments of the pad, as will be furtherdiscussed herein, the pad includes not only a heating element, but mayalso include foam, or could also be air bladders of (e.g., mattresscomponents) that are easily deformable to allow the patient to sink intothe pad. This accommodation increases the area of the patient's skinsurface in contact with the heated pad and minimizes the pressureapplied to the patient at any given point. It also increases the surfacecontact area for heat transfer and maximizes blood flow to the skin incontact with the heat for optimal heat transfer. Unlike conventionalpatient warming systems, the accommodation of the patient into the padis not hindered by a stiff, non-conforming, non-stretching, hammockingheating element. Additionally, in various embodiments, the heatingelement is at or near the top surface of the underbody support, inthermally conductive contact with the patient's skin, not locatedbeneath thick layers of foam or fibrous insulation.

Various embodiments further provide improved safety. For example, someembodiments provide a heating element that does not produce or reduces“pressure points” against the patient's body, such as against bonyprominences, which can occur when a heated pad (or blanket) is stiff.

FIG. 12 depicts a cross section of a portion of a heater assembly 1. Insome embodiments, the heater assembly 1 (e.g., may be same or similar toheating blanket or pad 100, or heating element assembly 350, or anyother heaters described herein) including a stretchable fabric heatingelement 10 (e.g., may be the same or similar to heating elements 310,502). This example shows the benefits of the stretchable heating element10, along with a compressible material layer 20 beneath the heatingelement 10 and bonded to the heating element 10 by a layer of adhesive30. The heater assembly 1 may include an upper shell 40 and a lowershell 42 (e.g., may be similar to sheets 504, 506). This construction ofthe heater assembly 1 is favorable because it curves smoothly underpressure from a patient's body (not shown) to stretch into an area ofcompound curve deformation 22.

In the embodiment shown in FIG. 12 and in several other embodiments, afoam layer 20 is included beneath the heating element 10 (e.g., 310 inFIG. 2A). However, the foam layer 20 may alternatively be described as alayer of compressible material in each of these embodiments and is notlimited to foam. For example, the layer of compressible material maycomprise gel, stuffing material such as polyester, polyester pellets,bean bag material such as polystyrene beads, air filled compartment, orany material that provides a flexible layer for patient accommodation.

Heat transfer is maximized when the heating element 10 is in conductivethermal contact with the patient. However, as described previously insome embodiments, at least one layer of plastic film is interposedbetween the heating element 10 and the patient to protect the heatingelement 10. The one or more layers of thin plastic film may form theupper sheet 40 between the heating element 10 and the patient tointroduce minimal thermal resistance to heat flow. In certainembodiments of this invention the fabric heating element 10 may belaminated between two layers of thin (<0.004 in.) and preferablystretchy (e.g. urethane or polyvinyl chloride) plastic films. Laminatinga thin layer of plastic film directly onto each side of the heatingelement 10 protects the heating element 10 fabric from damage by liquidsand oxidation. Thin layers of plastic film are sufficient to protect theheating element 10 from liquid and gases, add minimal if any stiffnessto the construction, and still allow the heating element 10 to stretchand return to its original shape. This is in contrast to some otherconductive fabrics which may require lamination between two thick layersof plastic film in order to provide structural strength and durability,resulting in a stiff and non-stretchable heater.

In some embodiments, the heating element 10 is coated with one or morethin layers of elastomeric materials such as rubber or silicone. Thelayers of elastomeric material protect the heating element 10 materialfrom damage due to moisture and oxidative chemicals such as hydrogenperoxide. The layers of elastomeric material also provide anelectrically insulating layer over the heating element 10 material.

In some embodiments the heating element 10 is also used as a groundingelectrode during electro-surgery, the upper layer of elastomericmaterial forms a second dielectric layer between the patient and theheater, adding to the safety of the device should the outer shellmaterial 40, 42 be cut or pierced. The second dielectric layer preventsa direct electrical contact between the patient and the groundingelectrode (e.g., 10).

The pressure relief provided by the pad is maintained by allowingmaximal accommodation (allowing the patient to sink into the support)without the heating element assembly creating a “hammocking” force. Byallowing maximal accommodation and avoiding hammocking, cutaneous bloodflow is maximized at the pressure points, which minimizes the risk ofpressure ulcers. The pressure needed to collapse capillaries is said tobe 12 to 32 mm Hg. By allowing maximal accommodation and avoidinghammocking, cutaneous blood flow is generally maximized. By maximizingblood flow, the ability of the skin and tissue to absorb heat from theheating element 10 and transfer it to the rest of the body is alsomaximized. Further, by allowing the patient to sink (accommodation) intothe heater assembly 1, the surface area of the heating element 10 incontact with the patient is maximized and thus heat transfer ismaximized.

When not stretched, fabric heating elements 10 as described hereinprovide an even heat output or Watt density across their surface, unlessthey are folded or wrinkled, doubling or tripling the heating element 10layers in the folded or wrinkled portion. The entire heating element 10may have a relatively low Watt density, such as less than 0.5 watts persquare inch, for example. Therefore, it is preferable to prevent localwrinkling of the heating element 10. An embodiment of a heated pad 2 inthe form of a heated underbody support, a heated mattress, or a heatedmattress overlay includes a heater assembly 1 and a compressiblematerial layer (e.g., foam layer) 20 and having reduced wrinkling orfolding is shown in FIG. 13 . It should be noted, however, that whethera unit is described as a heated mattress, heated mattress overlay orheated pad is largely unimportant, and most embodiments could be usedvariously as heated underbody supports. While a heated mattress overlayor blanket may have no layer of padding or may have a thinner layer ofpadding, a heated pad typically has padding that may be thin or thick, aheated mattress may have an even thicker layer of padding. As such,various embodiments of the pad may be used alone, in the manner of amattress, or on top of a mattress, in the manner of a mattress overlay.Descriptions relating to heated mattress overlays therefore also applyto descriptions of heated mattresses and heated pads, and vice versa.

The compressible material layer 20 (e.g., FIG. 13 ) may be a singlelayer or may be a stack of materials that includes a layer of foam. Thisstack could include foam layers of different densities, differentaccommodation properties, different stiffness or different polymers.Additionally, the stack of materials can include other materials such aswoven or non-woven fabrics or films, to achieve other characteristicssuch as lateral stiffness or durability and strength. The termcompressible material layer 20 therefore refers generally to singlelayers of foam as well as multilayered stacks that include one or morelayers of foam and may include other materials. Also, the layer of foammay alternatively be a layer of compressible material as describedabove.

As shown in FIG. 13 , the attachment of the heating element 10 to thecompressible material layer 20 may be achieved by adhesive bonding 30across the entire interface between the two. The bond may be made withan adhesive comprising a pressure-sensitive adhesive without areinforcing fiber or film carrier. Since the compressible material layer20 is preferably flexible, stretchable and compressible, such a bondingmade with such an adhesive does not alter the flexibility andstretch-ability of the heating element 10 or heated mattress overlay orpad 2. Alternately, the heating element 10 may be attached to thecompressible material layer 20 only along one or more of the edges 12,14, 16, 18 (16 and 18 not shown in FIG. 13 , but similar and generallyperpendicular to edges 12 and 14). In some embodiments the heatingelement 10 may be attached to the compressible material layer 20 onlyalong one or more edges such as along two opposing edges such as edges12, 14, or in an intermittent pattern.

FIG. 14 depicts a cross section of a portion of an alternativeembodiment of a heated pad 2, in which the fabric heating element 10 andthe overlaying plastic film layer comprising an upper shell 40 include asacrificial layer of fabric or foam 74, inserted there between. Thesacrificial layer of fabric or foam 74 is preferably treated withmanganese dioxide (MnO2) to act as a catalyst in the destruction ofhydrogen peroxide cleaning fluid vapor that may permeate the upper shellmaterial 40 and enter the shell where it can damage the electricalcomponents.

An alternative embodiment is shown in the heated pad 2 which is shown inFIG. 15 . In this embodiment, the fabric heating element 10 is anchoredto the shell including the upper shell 40 and the lower shell 42 alongits edges and thus held in an extended and wrinkle-free condition.Anchoring strips 46 comprised of plastic film or a suitable alternativeare attached along the edges of the heating element 10, preferably bysewing to form a sewn connection 85, though other forms of attachmentmay be used such as adhesive bonding. The anchoring strips 46 extendalong all four edges of the heating element 10 to form a peripheral bond48. Alternatively, the anchoring strips 46 may extend along only onepair of opposing edges such as edges. The anchoring strips 46 may bemade of the same material as the shells 40, 42, such as plastic film,and therefore can be bonded around the periphery of the heated pad 2,being sandwiched between and incorporated into the bond between theupper shell 40 and the lower shell 42.

Hydrogen peroxide (H₂O₂) disinfecting solutions have recently beenintroduced into the operating room and hospital to clean and sanitizemedical equipment. H₂O₂ is a well-known, powerful oxidizing agent thatkills bacteria and viruses in a mechanical way that cannot lead toresistant strains. The oxidation reaction causes the H₂O₂ to break downinto water and oxygen, two harmless, or less harmless by-products. Theproblem is that H₂O₂ vapor is also highly oxidizing for electricalcomponents, including flexible heater materials (including polypyrrole),metal bus bars and conductive metal coatings such as silver on fabric orthread. There is a need for better protection of the sensitiveelectrical components from oxidation by H₂O₂ and other oxidizers.

In some embodiments, urethane film may be used as the shell 40, 42material for the heated pad 2 or related blankets, because of itsstrength, flexibility durability and response to heat sealing.Unfortunately, although urethane film may be good for providing awater-resistant and encapsulating shell 40, 42, urethane film isrelatively permeable to hydrogen peroxide vapors, allowing the highlyoxidizing vapors to enter the heated pad 2 or a related heated electricblanket. Once inside, the peroxide vapors attack any oxidizablematerial. These vapors can cause oxidation and failure of electricalcomponents, especially polypyrrole. Other plastic films such as PVC aremuch less permeable to peroxide vapor than urethane. Since peroxide isbecoming more and more common as a disinfectant for operating room andother hospital use, a way of protecting vulnerable internal componentsfrom oxidation due to peroxide is needed.

In some embodiments, the heated pad 2 or the related heated electricblankets incorporate certain materials that can protect the polypyrroleheater (e.g., heating element 10) and other oxidizable electricalcomponents from oxidizing agents such as hydrogen peroxide (H₂O₂)disinfecting solutions. In some embodiments, a catalyst to acceleratehydrogen peroxide decomposition may be coated on or impregnated into anelement within the shell 40, 42, or on the interior surface of the shell40, 42.

In some embodiments, sacrificial materials may be included in theinternal construction that can be preferentially oxidized. Sacrificialmaterials may be organic materials such as cellulose. For example,sacrificial materials such as one or more sacrificial layers 74 ofcotton, linen or paper, as shown in FIG. 14 , may be added to the insideof the heated pad 2 or the related heated electric blanket so that theperoxide vapors preferentially attack and oxidize the sacrificialmaterial. Other oxidizable sacrificial materials may be used. In theprocess of oxidizing these sacrificial materials, the peroxide breaksdown into inert (e.g., less corrosive, less problematic) water andoxygen before it can attack the electrical components. The catalyst foraccelerating hydrogen peroxide decomposition may decompose all,substantially all, or the majority of the hydrogen peroxide vaporsbefore they reach the electrical components, depending on how thecatalyst is incorporated into the particular apparatus.

In some embodiments, materials that are known to be catalysts for thebreakdown reaction of peroxide to water and oxygen may be added. Forexample, manganese dioxide (MnO₂) powder may be added to one or more ofthe sacrificial layers 74 in FIG. 14 , or the compressible materiallayer 20, the inside surface of the shell 40, 42, or adhered directly toany suitable component of a heater assembly 3 (e.g., FIG. 25 ) by anapplied coating, by impregnation into, by adhesive, or by any othersuitable process. Catalysts for the breakdown reaction of peroxide towater and oxygen may be added to any heater assembly, or any suitablecomponent of any of the heater assemblies described herein.

In some embodiments, the insoluble manganese dioxide powder may besuspended in water and the sacrificial layer 74 of fabric or foam can bedipped in this water/manganese dioxide powder suspension to evenlydisperse the powder throughout the sacrificial layer 74 of fabric orfoam when the water evaporates. In some embodiments, a small amount ofmethyl cellulose can be added to the water/manganese dioxide powdersuspension in order to increase the duration of the suspension time ofthe powder in water. The small amount, or sufficient amount of methylcellulose to increase the viscosity of the water and manganese dioxidesuspension to between 10 and 120 centipoise. The methyl cellulose mayalso act as a binding agent, improving adherence of the manganesedioxide powder to the fabric, foam or other material. Other bindingagents, and/or suspension improvers besides methyl cellulose may beused. Adding too much binding agent (e.g., greater than 120 centipoise)can cause the binding agent to completely encapsulate the manganesedioxide powder when it dries, and too little (e.g., less than 10centipoise) will not hold the powder in suspension very long. Othercarriers besides water may also be used.

In some embodiments, the one or more sacrificial layers 74 of manganesedioxide impregnated fabric or compressible material layer 20 may beadded to the inside of the pad 2 or related heated electric blanket sothat the catalyst can preferentially attack the peroxide vapors andneutralize them to water and oxygen, before they can damage theelectrical components. Other liquids are anticipated for suspending themanganese dioxide powder. Examples of catalysts that can be used inplace of manganese dioxide powder include: silver, platinum andtransition metal salts. Other catalysts may also be used. In someembodiments the catalysts may be added to another feature of the pad 2or the related heated electric blanket, and to a material other thanfabric or foam.

The effectiveness of these measures for preventing the oxidation anddegradation of the heater fabric (e.g., heating element) and othermattress or blanket components by peroxide vapor was tested. Duringtesting similar squares of heater material with bus bars attached weresealed into shells of urethane film. The heaters (e.g., heating pad orblanket) were then placed into a chamber that continuously exposes theshell to peroxide vapor. Over the course of 9-12 days, the change inresistance of the heater material was measured and correlated with thedegradation of the conductance of the heater material. Over the courseof 9 days of exposure to peroxide vapor, the resistance of unprotectedpolypyrrole heater material increased from 58.4 to 238.2 ohms on thesquare. The significant increase in resistance, indicates that theconductivity of the unprotected conductive heater material (e.g.,heating element 10) was rapidly degraded by the peroxide vapors.

Over the course of 12 days of exposure to peroxide vapor, the resistanceof heater assemblies that included two layers of sacrificial cottonfabric inside the shell, increased from 53.5 to 84.8 ohms on the square.Over the course of 12 days of exposure to peroxide vapor, the resistanceof heater assemblies that included two layers of polyester fabricimpregnated with manganese dioxide inside the shell, did not increaseresistance at all (52.8 to 52.8 ohms on the square). The MnO₂ was veryeffective as a catalyst neutralizing the peroxide vapor before it coulddestroy the heater assembly. The sacrificial layer of cotton fabric wasalso quite effective in protecting the heater assembly but less so thanthe MnO₂.

This disclosure of using MnO₂ or sacrificial cellulose layers to protectoxidizable components, especially electrical components, is not limitedto heated underbody supports (e.g., heated pads) 3 and heating blankets.In some embodiments, other medical equipment (e.g., apparatus) includingelectrical components such as patient monitors, patient monitoringelectrodes, patient monitoring sensors and medical equipment controlcircuits may be protected from oxidation and damage by peroxide vaporsor liquid, by incorporating MnO₂ or sacrificial cellulose layers intothe equipment, as disclosed in this application.

Some embodiments maintain the heating element 10 in an extended andunwrinkled condition. It may be preferable in order to avoid hot spots,that more than one heating element 10 anchoring embodiment be usedsimultaneously. To maintain flexibility, conformability andstretchability, the upper and/or lower shell 40, 42 may be adhered tothe heating element 10 or the compressible material layer 20, acrosstheir broad surfaces as shown, for example, in FIG. 14 , or may not beso adhered. However, in some embodiment the heating element 10 can bebonded to the upper shell 40, for example. This may be advantageous forminimizing wrinkling of the heating element 10 or plastic film layer ofthe shell 40, 42.

The compressible material layer 20 (or layer of compressible material)supporting the heater assembly 1 in certain embodiments of thisinvention could be almost any thickness that is advantageous for thegiven application (for example, 0.5-6.0 inches). The compressiblematerial layer 20 may be uniform in thickness and density or it may becontoured in thickness, shaped, scored or segmented according to areasof different densities.

As shown in FIGS. 16-18 , the portions of the heating element 10attached to bus bars 62, 64, which may include any of the featuresdescribed with respect to bus bars 315. In the exemplary embodiment ofFIGS. 16-18 , bus bars 62, 64 are preferably bonded to the compressiblematerial layer 20 along beveled ends 22, 24. Locating the bus bars 62,64 on the beveled ends 22, 24 of the foam layer 20 provides someprotection of the bus bars 62, 64 from mechanical stress when patientsare sitting or lying on the heated pad 2. Alternatively, to provideadditional protection to the bus bars 62, 64, the heating element 10 maybe wrapped around the compressible material layer 20 and onto a bottomsurface 23 so that the bus bars 62, 64 are located under the foam layerbeveled ends 22, 24 and attached to the bottom surface 23 as shown inthe cross section shown in FIG. 17 , for example. In a furtheralternative shown in FIG. 18 , the beveled piece of compressiblematerial that is removed from the compressible material layer 20 or anyother triangular or wedge shaped piece of compressible material ofcomplementary size and shape to fit the space may be bonded over theheater assembly's bus bars 62, 64, along the beveled edges 22, 24 of thecompressible material layer 20 to form a filler 25, to fill in thebeveled space and protect the bus bars 62, 64. The compressible materialfiller 25 may be sized such that, when in place above the bus bars 62,64, the horizontal upper surface of the heated pad 2 above the central,non-beveled portion of the compressible material layer 20, is level withthe horizontal upper surface of the overlay 2 above the beveled end 24.In these embodiments the heating element 10 extends across an uppersurface 21 of the compressible material layer 20, and the bus bars 62,64 are away from and lower than the upper surface 21. In this way, thebus bars 62, 64 may be physically protected from damage by bonding themonto or beneath the beveled edges 22, 24 of the compressible materiallayer 20, where they are effectively recessed from the upper surface 21of the foam layer 20. The beveled edges 22, 24 of the compressiblematerial layer 20 allow the bus bars 62, 64 to be optionally coveredwith a compressible material filler 25 to act as a protective barrier inthis location for added protection, without adversely affecting the lookof the smooth top surface of the heated pad 2, thereby basically fillingthe bevel space with a compressible material filler 25 to create anoverall rectangular cross sectional shape.

In some embodiments, the combination of conductive fabric heatingelements 10 made from flexible and stretchable material, bus bars 62, 64attached near opposing edges 12, 14 of the heating element 10, one ormore temperature sensors and a controller, comprises a heater assembly 1according to some embodiments. The heater assembly 1 may be secured to acompressible material layer 20 such as foam and may be covered with awater-resistant shell 40, 42 that is preferably made of a stretchableplastic film such as urethane or PVC, however, other film materials andfiber-reinforced films are anticipated.

In some embodiments, a portion of the compressible material layer 20 isthinned or scored in an area, from one lateral edge to the other of thearea, with the area located to overlie the location of transition fromone cushion of an operating table to the adjacent cushion under normalconditions of use. Preferably the thinning or scoring is on the bottomsurface 23 of the compressible material layer 20 and therefore away fromthe patient contact top surface 21. Since operating room tables aredesigned to flex at this location between the operating table cushions,a thinned compressible material layer 20 at the location of transitionbetween cushions will aid in flexion of the heating element 10 andreduce the chances of the heating element 10 wrinkling during flexion.Alternatively, the compressible material layer 20 could be scored or cutor otherwise have one or more gaps or channels completely through orpartially through its thickness on the bottom surface 23 at the flexionlocations or other areas where added flexibility may be desirable, asshown in FIG. 19 , for example. In the embodiment shown, multiple smallchannels 27 are present in a portion of the compressible material layer20 where the compressible material layer 20 is thinner. These channels27 may extend across the compressible material layer 20, from one end tothe opposing end, such as across the width or the length of thecompressible material layer 20, such as in a direction parallel to andaligned with the transition between operating table cushions. In use,the pad 2 may be positioned over a table or bed with which it isdesigned to be used such that the channels are located over the flexionlocations of the table or bed. The table or bed may then be adjusted bybending at a flexion point (such as to raise or lower a patient's upperbody or legs by bending or extending the patient at his or her hips) andthe compressible material layer 20 of the heated pad 2 can bend easilyat this location due to thinness or scoring at the location of flexion,while the heating element 10 can likewise bend without wrinkling orfolding due to its flexibility and elasticity.

In some embodiments, and as shown in FIG. 19 , the compressible materiallayer 20 may be thinned or scored or have gaps or channels 27longitudinally in order to increase flexibility for bending the heatedpad 2 around a longitudinal axis such as a long axis of a body. This maybe advantageous to aid in wrapping the heated pad 2 around a patientbeing positioned within a “bean bag” or “peg board” positioner. Thelongitudinal thinning or scoring or presence of gaps or channels 27allows the heated pad 2 to be wrapped around the dependent portion ofthe patient, increasing the area of surface contact between the heatingelement 10 and the skin while avoiding wrinkling of the heating element10 due to the bending of the compressible material layer 20.

In some embodiments, a heated mattress for pediatric use 100 may includean upper heated layer 102 that is separate from the lower base layer 104as shown in FIGS. 20, 21 and 22 A-D. The upper heated layer may alsoinclude a layer of thermal insulation material 106, preferably locatedon the underside of the heater element 10, away from the patient contactsurface. Preferably the thermal insulation layer 106 is a high-loftfibrous insulation, for example Thinsulite™ (3M, St. Paul, Minn.).

As shown in FIG. 20 , and in some embodiments, the upper heater layer102 is attached to a lower base layer 104 in a way that maintains thealignment of the upper heated layer 102 as it rests on the lower baselayer 104 yet allows maximal independent flexion between the two layers.The preferred attachment location between the two layers 102, 104 is atthe foot end periphery of the mattress 2. Alternately, it could be thatthe two layers 102, 104 are attached to each other at the head end or ina central region such as along a longitudinal centerline. These examplesare not meant to limit other areas of attachment between the two layers102, 104. The heater layer 102 is not bonded to the base layer acrosstheir entire opposing surfaces or around their entire peripheries. Thetwo layers 102, 104 are free to fold and bend substantiallyindependently of one another (FIGS. 20, 21 and 22A-D).

Maintaining the alignment of the two layers 102, 104 helps assure thatthe heater layer 102 does not slip, perhaps dropping the patient off ofthe bed. Surgical mattresses are frequently attached to the surgicaltable and in certain embodiments of this invention, preferably only thebase layer is attached to the table. The attachment between the twolayers 102, 104 may be secure enough to assure that the upper heatedlayer 102 cannot slide independently of the base layer 104.

In some embodiments, the base layer 104 may include two or moreelongated longitudinal air bladders 108 near the side edges. The airbladders 108 can be inflated to elevate the sides of the heated layer toa position proximate the side of the patient.

If the attachment between the two layers is not in the longitudinalmidline, patient-positioning rolls may be placed under the heated layerto maintain maximal heat transfer characteristics while allowing complexpatient positioning. For example, small rolls of towels are frequentlyplaced under the chest/shoulder blades of very small babies in order toput their back into extension and improve access to their upper abdomen.If this positioning roll is placed above the standard heated mattress,the roll lifts half of the patient's body off of the heated surface.Naturally this markedly reduces the heat transfer and capacitivegrounding ability of the mattress to the patient. In contrast, thisinvention allows the positioning roll to be placed under the upperheated layer and the heater thus stays in conductive thermal contactwith the entire posterior surface of the patient also maximizinggrounding contact.

It has been shown that for optimally safe and effective electricmattress warming, it is believed that the control temperature sensor 114(FIG. 21 ) desirably is touching the patient. Therefore, the controltemperature sensor is preferably located near the longitudinal midlineof the mattress, where the patient is most likely to lay as shown inFIG. 15 . It is easy to assure control sensor contact with an adultpatient because they cover most of the surface of the mattress (on anarrow operating table). However, small pediatric patients can easily bemal-positioned on the mattress and thus inadvertently fail to contactthe control temperature sensor.

In some embodiments, the flexible heating element 10 itself may comprisea temperature sensor. In such embodiments, the flexible heating element10 is formed of a material having a resistance that varies withtemperature. The controller may determine the temperature of theflexible heating element 10 by measuring the resistance or change inresistance in the power supply circuit. The resistance of the heatingelement 10 may also be used to determine the Watt density output of theheating element 10. Thus, the heating element resistance measurement maybe used as a control parameter by the controller to control or adjustthe Watt density output of the heated underbody support 2 as desired.

The combination of conductive fabric heating elements 10 made fromflexible and stretchable material, bus bars 62, 64 attached nearopposing edges 12, 14 of the heating element 10, one or more temperaturesensors 110 and a controller, comprises a heater assembly 1 according tosome embodiments. The heater assembly 1 may be secured to a compressiblematerial layer 20 such as foam and may be covered with thewater-resistant shell 40, 42 that is preferably made of a stretchableplastic film such as urethane or PVC, however, other film materials andfiber-reinforced films are anticipated.

To assure accurate patient positioning relative to the controltemperature sensor, this invention preferably includes two or moresubstantially elongated positioning members 108 that protrude upwardbetween 0.75 and 2.5 inches from the upper surface of the base layer(FIGS. 14, 15, 16A). The elongated positioning members 108 arepreferably made of a compressible foam material. The elongatedpositioning members 108 are preferably triangular in cross-section, are4-12 inches long and positioned 5 to 8 inches apart (2.5-4 inches fromthe midline) in the region of the mattress the corresponds to thelocation of the patient's torso and legs.

These parallel elongated positioning members 108 project upward into theupper heated layer, causing the upper heated layer to form a troughbetween the positioning members. The midline trough naturallyaccommodates the baby's body and centers it on the midline (FIGS. 15, 16). If the baby is not centered in the midline of the trough, the foampositioning members 108 will cause the baby to be visibly contorted,alerting the surgical staff that repositioning is required.

In addition to the warming features described herein, in someembodiments and as shown in FIG. 13 , the heating element 10, which isalready in close proximity to the underside of the patient, is acapacitive coupling grounding electrode 10. By using the heating elementmaterial 10 as the grounding electrode 10, there is no competition todetermine which technology is going to be in the most advantageousposition—close to the patient's skin. Both technologies get the sameadvantageous location. Using a single piece of conductive material,preferably a stretchable conductive or semi-conductive fabric as theheating element 10 and grounding electrode 10, also minimizes thenegative effects of multiple layers of materials and laminates beinginterposed under the patient, which can cause hammocking, therebyreducing the pressure off-loading abilities of the mattress. The fewerthe layers of material, the more stretchable and flexible theconstruction. Avoiding constructions that involve layers of fabric andfilm to be bonded together forming laminates is performed in order tooptimize stretchablity and flexibility.

A semi-conductive polymer such as polypyrrole is advantageous in that itis a preferential RF energy absorber. Polypyrrole can also bepolymerized onto fabric and in the process coats each individual fiber,retaining the flexibility and stretchability of that fabric. Thepolymerization process results in a bond between the fiber and thepolymer that is inseparable. This is in contrast to electricallyconductive composites made from powdered or vaporized carbon or metalsthat may be applied to the surface of relatively non-stretching fibersand fabrics such as woven nylon, because such composites will flake offwith repeated flexion and stretching. Polypyrrole is, therefore, apreferable conductive material for heaters and grounding electrodes thatare to be positioned under a patient because it allows flexion andstretching so that the patient can sink optimally into the supportsurface below the heating element and/or grounding electrode (e.g., 10).

As shown in FIG. 13A, in some embodiments the grounding electrode 50 isa separate layer of material positioned near and parallel to the heater10. In this case, the grounding electrode 50 may advantageously be madeof a semi-conductive polymer such as polypyrrole irrespective of whatthe material the heating element 10 is made. The heating element 10 andgrounding electrode 50 may be electrically insulated from each other byapplying a coating of elastomeric material 12 such as silicone or rubberto one or both conductors. A layer of electrically insulating material14 such as fabric, film or foam may be interposed between the heatingelement 10 and grounding electrode 50. Preferably these layers ofelectrically insulating materials are not all bonded together into alaminate that would add unnecessary stiffness to the support surface.

As shown in FIG. 13B, in some embodiments, the grounding electrode 50 isits own layer of material, and there is no heater (e.g., heating element10). In these cases, the grounding electrode may advantageously be madeof a semi-conductive polymer such as polypyrrole because of itsflexibility, stretchability, durability, radiolucency andradar-absorbing attributes, compared to other metal coated fabrics.

In certain embodiments of the invention as in FIGS. 13A and 13B, thegrounding electrode 50 is electrically connected via an electricalconductor, or bus bar 68. The bus bar 68 of some embodiments of thisinvention may be attached to the grounding electrode 50 by sewing withelectrically conductive thread. This construction maintains flexibilityand durability with repeated flexing. The sewn connection between thebus bar 68 and the grounding electrode 68 according to embodiments ofthe invention results in a connection that is very robust, flexible andtolerant of extreme flexing and resistant to degradation.

According to some embodiments, the bus bar 68 is coupled to thegrounding electrode 68 by a stitched coupling, for example, formed withelectrically conductive thread such as silver-coated polyester or nylonthread (Marktek Inc., Chesterfield, Mo.), extending through thegrounding electrode (e.g., 10 or 50) and through the bus bar 68.Alternative threads or yarns employed by embodiments of the presentinvention may be made of other polymeric or natural fibers coated withother electrically conductive materials. In addition, nickel, gold,platinum and various conductive polymers can be used to make conductivethreads. Metal threads such as stainless steel, copper or nickel couldalso be used for this application. According to an exemplary embodiment,the bus bar 68 may be comprised of flattened tubes of braided wires; forexample, a flat braided silver coated copper wire, and may thusaccommodate the attaching thread extending there through, passingthrough openings between the braided wires thereof. In addition, suchbus bars 68 are flexible, thereby enhancing the flexibility of themattress heater assembly. According to alternate embodiments, the busbar 68 may be a conductive foil or wire, flattened braided wires notformed in tubes, an embroidery of conductive thread, a printing ofconductive ink, or other suitable bus bar construction.

In some embodiments, the dielectric is the outer shell material 40 ofthe underbody support (mattress overlay or pad 2). In some embodiments,other layers of material such as fabric or foam 74 (FIG. 14 ) may beinterposed between the shell dielectric material 40 and theheater/grounding electrode material 10. In some embodiments, theselayers of materials are preferably not laminated together, therebymaintaining maximal flexibility and stretchablity for accommodating thepatient into the pad 2.

In some embodiments, one or both sides of the grounding electrode layer10, 50 (and/or heating element 10) is coated on its upper side with athin layer of flexible, stretchable elastomeric material such as rubberor silicone. This coating of elastomeric material interposed between theelectrode and the dielectric material layers serves as second,redundant, safety dielectric layer should an inadvertent hole be putinto the outer shell. The redundant dielectric layer would preventdirect electrical coupling between the patient and the groundingelectrode material 10, 50, which could cause a burn.

Preferably, the elastomeric material is applied as a gel or liquid sothat it can coat the individual fibers of the heating element material(e.g. 310, 502, 10) before it sets up into its elastomeric solid form.Coating the individual fibers maximally protects the heating element,from moisture damage. It also limits the electrical contact area to aninadvertently cut edge in the exceedingly unlikely event that the boththe dielectric and heater layers are cut and the active electrode of theelectrosurgical unit is inserted into the cut. In this instance thepolymeric heaters fibers at the cut edge would melt and retract from theelectrode, automatically limiting the adverse current flow.

In some embodiments, the return electrode wire 70 is electricallyconnected 72 directly to the grounding electrode material 10. Since thegrounding electrode 10 is the heating element 10, the electrode itselfadds resistance to the current flow through the circuit. The further thecurrent may flow through the heater material, the greater theresistance. A return electrode wire 70 connected 72 to one end of theheating element 10 would create a situation wherein the electricalresistance to current flow would be significantly greater for currentoriginating at the far end compared to the end of the patient closest tothe wire connection 72.

In some embodiments, the return electrode wire 70 is electricallyconnected 72 to one of the bus bars 62, 64. Connecting the returnelectrode wire 70 to the bus bar 62 or 64 is advantageous when thegrounding electrode material is a resistive heating element 10 that addsresistance to the circuit. Since the low resistance bus bar 62, 64 runssubstantially parallel to the patient along an edge of the groundingelectrode, the resistance to the current flow caused by the heatermaterial is substantially equal along the entire length of the patientthat is contacting the grounding electrode creating a safe condition.

In some embodiments, the shared conductive pathway through the heatingelement 10 involves that the capacitive coupling electrode of theinstant invention be adapted to hook to patient warming power suppliesand electrosurgical generator that are designed with a “floating”output. By “floating,” we mean that the electrical current within eachof the respective circuits has no potential or reference with respect toearth (ground) or with respect to the other piece of equipment. Thisconfiguration allows simultaneous operation of the patient warming powersupply and electrosurgical generator without electrical interferenceoccurring between the two.

In some embodiments, the shared conductive pathway through the heatingelement 10 may require that the capacitive coupling electrode of theinstant invention be adapted to hook only to patient warming powersupplies that supply a low voltage direct current (48 volts or less) andan electrosurgical unit that supplies an RF current. This configurationhelps to allow simultaneous operation of the patient warming powersupply and electrosurgical unit without electrical interferenceoccurring between the two.

In FIGS. 12 and 16 , the shell 40, 42 protects and isolates the heaterassembly 1 from an external environment of the heater assembly 1 and mayfurther protect a patient disposed on the heated pad 2 from electricalshock hazards. According to preferred embodiments, the shell 40, 42 iswaterproof to prevent fluids, for example, bodily fluids, IV fluids, orcleaning fluids, from contacting the heater assembly 1, and may furtherinclude an anti-microbial element, such as SILVERion® antimicrobialfabric available from Domestic Fabrics Corporation (Kinston, N.C.),which is extruded in the plastic film of the shell material.

As shown in FIGS. 15 and 16 , in some embodiments, a layer of plasticfilm is placed over each broad surface of the heater assembly 1, as anupper shell 40 and a lower shell 42 but is not bonded to the heaterassembly 1. The two layers of plastic film are bonded to each otheraround a periphery 48 of the heater assembly 1 to form a water-resistantshell. The bond may be from heat, radio frequency (RF), ultrasound,solvent or adhesive, for example. The heater assembly 1 may be “freefloating” within the shell with no attachment to the shell, or can beattached to the shell, such as only at the edges of the heater assembly1 as described above, for example. This bond construction around theperiphery 48 of the heated pad 2 creates a durable shell without folds,creases, crevasses or sewing needle holes that can collect infectiousdebris and be difficult to clean. The heater assembly 1 covered by ashell of plastic film and optionally including a foam or other supportlayer comprises a heated mattress, mattress overlay, or pad according tosome embodiments.

FIG. 23 depicts a cross section of a portion of an alternativeembodiment of a heated pad 2, in which the fabric heating element 10 isbonded to an overlaying plastic film layer comprising an upper shell 40by a layer of adhesive 35. In such embodiments, the upper shell 40 canbe stretched and held in position by the compressible material layer 20or by anchoring the heated pad 2 laterally, with or without bonding theshell 40, 42 to the heating element. When the stretched layer of uppershell material 40 is bonded to the heating element 10, this may reduceor prevent wrinkling or folding of the heater element 10 and yetmaintain flexibility and stretchability (depending on the stretchabilityof the shell material). In the embodiment shown, the heated pad 2further includes a lower shell 42 beneath the compressible materiallayer 20.

In certain embodiments, such as the embodiments shown in FIGS. 23 and 24, the shell construction allows a power entry module 130 to be locatedand bonded between the shell, such as the layers of plastic film 40, 42,at the edge of the shell within the bonded layers 48. The power entrymodule 130 can be bonded with adhesive, solvent or heat, for example,between the adjacent layers of upper and lower shell 40, 42. Sewn shellconstructions known in the art prevent the power entry from beinglocated at the sewn edge and result in the power entry being located onthe flat surface of the shell rather than the edge, which may result inthe patient laying on the hard lump created by the power entry moduleand which could contribute to the formation of a pressure injury. Insome embodiments, the power entry module 130 is a piece of moldedplastic, for example in a shield-shape, that can be sealed between thesheets 40 and 42 in the peripheral bond 48 edge seal of the shells 40,42. The pointed ends of the shield-shaped power entry module 130 allowsthe shells 40, 42 to transition smoothly from the area where the upperand lower shells 40, 42 are sealed to each other, to the adjacent areawhere the shells 40, 42 are sealed to the power entry module 130 andthen back to the shells 40, 42 being sealed to each other. In someembodiments, the power entry module 130 includes a tubular channel 132traversing from the outer side to the inner side of the shell. Thetubular channel 132 may be sized to accommodate a wire cable 134 thatcontains the power and sensor wires. The wire cable 134 can pass throughthe tubular channel 132 from the outside to the inside of the heated pad2 and can be adhesive, solvent or heat bonded to the power entry modulein this position, creating a water-tight seal. In another embodiment,the power entry module 130 may be shaped and sized to house a plug-inconnector. In some embodiments, the return electrode wire 70 thatconnects to the electrosurgical generator can pass through an identicaltubular channel 132 from the inside to the outside of the heated pad 2as the power entry module 130, which is used for the power cable 134 toexit the shell.

The heated underbody support may have two or more attachment points suchas tabs 140 for securing the support over the top of a surgical mattressor table such as is shown in FIG. 23 . These attachment points may betabs 140 or flaps made from shell material that extend outward from theperipheral bond 48 of the shell. These attachment points may befiber-reinforced and yet flexible and somewhat loose, so that they donot cause hammocking of the shell. The attachment points can be securedto the table with many different means including straps, ties, loops,hooks, snaps, barbs, Velcro or other attachment means.

The heater assembly 1 of these inventions can be encased in a shell ofplastic film as described, or may have no shell. With or without a shellor compressible material layer 20, it can be used alone, or it can beused as a mattress overlay on top of, or can be inserted into, apressure reducing mattress. For example, since pressure reducingmattresses typically have water resistant covers, the heater assembly 1may be inserted directly into the mattress, inside the mattress cover,without a shell on the heater assembly 1. In either case, the heaterassembly 1, or heated pad 2 is designed to have little or no negativeimpact on the pressure reducing capabilities of the mattress on which itis laying or into which it is inserted.

The heated pad 2 may have two or more attachment points such as tabs 140for securing the support over the top of a surgical mattress or tablesuch as is shown in FIG. 24 . These attachment points may be tabs 140 orflaps made from shell material that extend outward from the peripheralbond 48 of the shell. These attachment points may be fiber-reinforcedand yet flexible and somewhat loose, so that they do not causehammocking of the shell. The attachment points can be secured to thetable with many different means including straps, ties, loops, hooks,snaps, barbs, Velcro or other attachment means.

The shell of the heater assembly 1 is preferably water resistant,flexible, and durable enough to withstand the wear and tear of operatingroom use. Examples of materials which may be used for the shell includeurethane and PVC. Many other suitable plastic film or fiber-reinforcedplastic film shell materials are anticipated. In some embodiments, theshell material is about 0.010-0.015 inch thick. In this thickness range,both urethane and PVC, for example, are strong but retain an adequatestretchability. The heated pad 2 may cover approximately the entiresurface of the surgical table or any other bed. Alternately, the heatedpad 2 may be sized to fit some or all of the cushion that form thesupport surface of a surgical table. For example, if the cushion hasmultiple separate sections, such as three, the heated pad 2 may be sizedto fit over one or two or all three of the cushion sections.

As shown in FIG. 25 , in some embodiments, compressible material layer20 or a foam layer 150 may be high tech foam to reduce the pressureexerted against the patient's skin during surgery. High tech foamsinclude but are not limited to visco-elastic foams that are designed tomaximize accommodation of the patient into the mattress (e.g., pad). Aspreviously noted, accommodation refers to the sinking of the user, suchas the patient, into the pad 2 until a maximal amount of support surfacearea is in contact with a maximal amount of skin surface, and thepressure exerted across the skin surface is as uniform as possible.These high tech foam materials may accommodate the patient moreeffectively than simple urethane upholstery foam. Unlike other mattressheaters or heating materials, the unique stretchable, flexible, freefloating design of the heater assemblies 1 described herein allow themto overlay a layer of visco-elastic foam and maintain the accommodationproperties of the foam. Further, the heater assembly 1 of this inventionis soft, flexible and stretchable enough to be the separated from thepatient by only a single layer of plastic film and still be comfortable.The avoidance of multiple layers of materials interposed between thepatient and the mattress foam maximizes accommodation and heat transfer.

In embodiments comprising heated mattresses 3 including foam layers 150,a water-resistant shell or cover 160 may encase the foam 150 as shown,for example, in FIG. 25 . The foam 150 may be simple urethane foam orhigh-tech foam such as visco-elastic foam, for example. The cover 160may be made of plastic film that has been extruded onto a woven fabric(e.g., Naugahyde), for example. In one embodiment, the heater assembly 1may be located within or may be removably inserted directly into themattress cover 160, with or without a shell 40 on the heater assembly 1.The heater assembly 1 may be placed directly on top of the mattress foam150 inside the cover 160 or a heater assembly 1 (with its own shell) maybe placed on top of a mattress outside of the mattress cover 160. If afoam mattress has its own shell, the thickness of the shell 40 of theheater assembly 1 can be reduced to, for example, about 0.003 and about0.010 inch, or even omitted, because the heater assembly 1 is protectedfrom mechanical damage by the cover 160 of the mattress 150. The thinnershell material improves the stretch-ability of the shell. Alternately,the heating element 10 may be bonded directly to the mattress foam 150.

The thermal effectiveness of this heated underbody support can beoptimized when the heating element 10 is overlaying a layer that canprovide maximal accommodation of the patient positioned on the support.In this condition, the heating element 10 is in contact with a maximalamount of the patient's skin surface which maximizes heat transfer.Heated pads made with inflatable air chambers forming or included in thecompressible material layer 20 or in addition to the compressiblematerial layer 20, can provide excellent accommodation. Further, aheated underbody support with excellent accommodation properties havinga heating element 10 as described herein avoids degrading theaccommodation properties of the mattress when a heater assembly 1 isadded.

In the foregoing detailed description, the invention has been describedwith reference to specific embodiments. However, it may be appreciatedthat various modifications, changes and alternative combinations can bemade without departing from the scope of the invention as set forth inthe appended claims. Although embodiments of the invention are describedin the context of a hospital operating room, it is contemplated thatsome embodiments of the invention may be used in other environments.Those embodiments of the present invention, which are not intended foruse in an operating environment and need not meet stringent FDArequirements for repeated used in an operating environment, need notincluding particular features described herein, for example, related toprecise temperature control. Thus, some of the features of preferredembodiments described herein are not necessarily included in preferredembodiments of the invention which are intended for alternative uses.

The invention claimed is:
 1. An electric heating pad for warming apatient comprising a heated underbody support, heated mattress or heatedmattress overlay comprising: a flexible sheet-like heating elementincluding an upper edge, a lower edge, and at least two side edges, theflexible sheet-like heating element configured to generate heat; a shellcovering the heating element and comprising at least two sheets offlexible material; and the at least two sheets of flexible materialcomprise a first sheet that is configured to be in contact with thepatient during warming, and a second sheet that is configured to bespaced apart from the patient during warming, and a layer of thermallyinsulating polymeric foam is positioned between the heating element andthe second sheet of the shell; and a weld coupling the two sheets offlexible material together about the upper edge, the lower edge, and theat least two side edges of the heating element, wherein the weld is oneof a RF weld, ultrasonic weld, or a heat bond; wherein the two sheets offlexible material each include at least one layer of PVC to facilitatethe one of the RF weld, the ultrasonic weld, or the heat bond.
 2. Theelectric heated underbody support, heated mattress or heated mattressoverlay of claim 1, wherein the layer of thermally insulating polymericfoam is laminated to the heating element with adhesive.
 3. The electricheated underbody support, heated mattress or heated mattress overlay ofclaim 1, wherein the layer of thermally insulating polymeric foam islaminated across a portion of its surface to the heating element withadhesive.
 4. The electric heated underbody support, heated mattress orheated mattress overlay of claim 1, wherein the flexible heating elementconforms to the contours of the body of the patient.
 5. The electricheated underbody support, heated mattress or heated mattress overlay ofclaim 1, wherein the edges of the heating element include a first sideedge and a second side edge; and a first conductive bus bar coupled tothe heating element and extending alongside the first side edge of theheating element, the first bus bar being adapted for coupling to a powersource for powering the heating element; and a second conductive bus barcoupled to the heating element and extending alongside the second sideedge of the heating element, the second bus bar being adapted forcoupling to the power source for powering the heating element; and theheating element is stitched to the first bus bar with a first row ofelectrically conductive stitching; and the heating element is stitchedto the second bus bar with a second row of electrically conductivestitching.
 6. The electric heated underbody support, heated mattress orheated mattress overlay of claim 5, further comprising: a firstelectrically insulating member interposed between the first conductivebus bar and the flexible heater and being secured therebetween by thefirst row of conductive stitching, the first electrically insulatingmember preventing direct electrical contact between the first conductivebus bar and the flexible heater; and a second electrically insulatingmember interposed between the second conductive bus bar and the flexibleheater and being secured therebetween by the second row of electricallyconductive stitching, the second electrically insulating memberpreventing direct electrical contact between the first conductive busbar and the flexible heater.
 7. The electric heated underbody support,heated mattress or heated mattress overlay of claim 1, wherein theheating element has a surface area of generally uniform electricalresistance per unit area such that the heating element produces asubstantially uniform watt density output across the surface area whenthe element is electrically powered; and further comprising: atemperature sensor coupled to the heating element at a first locationthereof where the heating element is configured and located to be inconductive contact with the body of the patient during warming, thefirst location defining a first temperature zone of the surface area ofthe element; and a temperature controller coupled to the temperaturesensor; and an electric power source coupled to the heating element andto the temperature controller, the power source being controlled by thecontroller, according to a sensed temperature of the first temperaturezone, as sensed by the temperature sensor, in order to maintain a firsttemperature of the first temperature zone lower than a secondtemperature of a second temperature zone of the surface area of theheating element, the second temperature zone being defined by a secondlocation of the heating element that is not in conductive contact withthe body during warming.
 8. An electric heating pad for warming apatient comprising a heated underbody support, heated mattress or heatedmattress overlay comprising: a flexible sheet-like heating elementincluding an upper edge, a lower edge, and at least two side edges, theflexible sheet-like heating element configured to generate heat; a shellcovering the heating element and comprising at least two sheets offlexible material; and the at least two sheets of flexible materialcomprise a first sheet that is configured to be in contact with thepatient during warming, and a second sheet that is configured to bespaced apart from the patient during warming, and a layer of thermallyinsulating polymeric foam is positioned between the heating element andthe second sheet of the shell; and a weld coupling the two sheets offlexible material together about the upper edge, the lower edge, and theat least two side edges of the heating element, wherein the weld is oneof a RF weld, ultrasonic weld, or a heat bond; wherein the two sheets offlexible material each include at least one layer of urethane tofacilitate the one of the RF weld, the ultrasonic weld, or the heatbond.
 9. The electric heated underbody support, heated mattress orheated mattress overlay of claim 8, wherein the layer of thermallyinsulating polymeric foam is laminated to the heating element withadhesive.
 10. The electric heated underbody support, heated mattress orheated mattress overlay of claim 8, wherein the layer of thermallyinsulating polymeric foam is laminated across a portion of its surfaceto the heating element with adhesive.
 11. The electric heated underbodysupport, heated mattress or heated mattress overlay of claim 8, whereinthe flexible heating element conforms to the contours of the body of thepatient.
 12. The electric heated underbody support, heated mattress orheated mattress overlay of claim 8, wherein the edges of the heatingelement include a first side edge and a second side edge; and a firstconductive bus bar coupled to the heating element and extendingalongside the first side edge of the heating element, the first bus barbeing adapted for coupling to a power source for powering the heatingelement; and a second conductive bus bar coupled to the heating elementand extending alongside the second side edge of the heating element, thesecond bus bar being adapted for coupling to the power source forpowering the heating element; and the heating element is stitched to thefirst bus bar with a first row of electrically conductive stitching; andthe heating element is stitched to the second bus bar with a second rowof electrically conductive stitching.
 13. The electric heated underbodysupport, heated mattress or heated mattress overlay of claim 12, furthercomprising: a first electrically insulating member interposed betweenthe first conductive bus bar and the flexible heater and being securedtherebetween by the first row of conductive stitching, the firstelectrically insulating member preventing direct electrical contactbetween the first conductive bus bar and the flexible heater; and asecond electrically insulating member interposed between the secondconductive bus bar and the flexible heater and being securedtherebetween by the second row of electrically conductive stitching, thesecond electrically insulating member preventing direct electricalcontact between the first conductive bus bar and the flexible heater.14. The electric heated underbody support, heated mattress or heatedmattress overlay of claim 8, wherein the heating element has a surfacearea of generally uniform electrical resistance per unit area such thatthe heating element produces a substantially uniform watt density outputacross the surface area when the element is electrically powered; andfurther comprising: a temperature sensor coupled to the heating elementat a first location thereof where the heating element is configured andlocated to be in conductive contact with the body of the patient duringwarming, the first location defining a first temperature zone of thesurface area of the element; and a temperature controller coupled to thetemperature sensor; and an electric power source coupled to the heatingelement and to the temperature controller, the power source beingcontrolled by the controller, according to a sensed temperature of thefirst temperature zone, as sensed by the temperature sensor, in order tomaintain a first temperature of the first temperature zone lower than asecond temperature of a second temperature zone of the surface area ofthe heating element, the second temperature zone being defined by asecond location of the heating element that is not in conductive contactwith the body during warming.
 15. An electric heating pad for warming apatient comprising a heated underbody support, heated mattress or heatedmattress overlay comprising: a flexible sheet-like heating elementincluding an upper edge, a lower edge, and at least two side edges, theflexible sheet-like heating element configured to generate heat; a shellcovering the heating element and comprising at least two sheets offlexible material; and the at least two sheets of flexible materialcomprise a first sheet that is configured to be in contact with thepatient during warming, and a second sheet that is configured to bespaced apart from the patient during warming, and a layer of thermallyinsulating polymeric foam is positioned between the heating element andthe second sheet of the shell; and a weld coupling the two sheets offlexible material together about the upper edge, the lower edge, and theat least two side edges of the heating element, wherein the weld is oneof a RF weld, ultrasonic weld, or a heat bond; wherein the two sheets offlexible material each include at least one layer of a weldablepolymeric material to facilitate the one of the RF weld, the ultrasonicweld, or the heat bond.
 16. The electric heated underbody support,heated mattress or heated mattress overlay of claim 15, wherein thelayer of thermally insulating polymeric foam is laminated to the heatingelement with adhesive.
 17. The electric heated underbody support, heatedmattress or heated mattress overlay of claim 15, wherein the layer ofthermally insulating polymeric foam is laminated across a portion of itssurface to the heating element with adhesive.
 18. The electric heatedunderbody support, heated mattress or heated mattress overlay of claim15, wherein the flexible heating element conforms to the contours of thebody of the patient.
 19. The electric heated underbody support, heatedmattress or heated mattress overlay of claim 15, wherein the edges ofthe heating element include a first side edge and a second side edge;and a first conductive bus bar coupled to the heating element andextending alongside the first side edge of the heating element, thefirst bus bar being adapted for coupling to a power source for poweringthe heating element; and a second conductive bus bar coupled to theheating element and extending alongside the second side edge of theheating element, the second bus bar being adapted for coupling to thepower source for powering the heating element; and the heating elementis stitched to the first bus bar with a first row of electricallyconductive stitching; and the heating element is stitched to the secondbus bar with a second row of electrically conductive stitching.
 20. Theelectric heated underbody support, heated mattress or heated mattressoverlay of claim 19, further comprising: a first electrically insulatingmember interposed between the first conductive bus bar and the flexibleheater and being secured therebetween by the first row of conductivestitching, the first electrically insulating member preventing directelectrical contact between the first conductive bus bar and the flexibleheater; and a second electrically insulating member interposed betweenthe second conductive bus bar and the flexible heater and being securedtherebetween by the second row of electrically conductive stitching, thesecond electrically insulating member preventing direct electricalcontact between the first conductive bus bar and the flexible heater.21. The electric heated underbody support, heated mattress or heatedmattress overlay of claim 15, wherein the heating element has a surfacearea of generally uniform electrical resistance per unit area such thatthe heating element produces a substantially uniform watt density outputacross the surface area when the element is electrically powered; andfurther comprising: a temperature sensor coupled to the heating elementat a first location thereof where the heating element is configured andlocated to be in conductive contact with the body of the patient duringwarming, the first location defining a first temperature zone of thesurface area of the element; and a temperature controller coupled to thetemperature sensor; and an electric power source coupled to the heatingelement and to the temperature controller, the power source beingcontrolled by the controller, according to a sensed temperature of thefirst temperature zone, as sensed by the temperature sensor, in order tomaintain a first temperature of the first temperature zone lower than asecond temperature of a second temperature zone of the surface area ofthe heating element, the second temperature zone being defined by asecond location of the heating element that is not in conductive contactwith the body during warming.
 22. The electric heated underbody support,heated mattress or heated mattress overlay of claim 15, furthercomprising: a catalyst to accelerate hydrogen peroxide decompositioncoated on or impregnated into an element within the shell, or on theinterior surface of the shell.
 23. An electric heating pad for warming apatient comprising a heated underbody support, heated mattress or heatedmattress overlay comprising: a flexible sheet-like heating elementincluding an upper edge, a lower edge, and at least two side edges, theflexible sheet-like heating element configured to generate heat; a shellcovering the heating element and comprising at least two sheets offlexible material; and the at least two sheets of flexible materialcomprise a first sheet that is configured to be in contact with thepatient during warming, and a second sheet that is configured to bespaced apart from the patient during warming, and a layer of thermallyinsulating polymeric foam is positioned between the heating element andthe second sheet of the shell; and a weld coupling the two sheets offlexible material together about the upper edge, the lower edge, and theat least two side edges of the heating element, wherein the weld is oneof a RF weld, ultrasonic weld, or a heat bond; wherein each sheet offlexible material comprises a strengthening layer and a second layer ofa weldable polymeric material to facilitate the one of the RF weld, theultrasonic weld, or the heat bond.
 24. The electric heated underbodysupport, heated mattress or heated mattress overlay of claim 23, whereinthe layer of thermally insulating polymeric foam is laminated to theheating element with adhesive.
 25. The electric heated underbodysupport, heated mattress or heated mattress overlay of claim 23, whereinthe layer of thermally insulating polymeric foam is laminated across aportion of its surface to the heating element with adhesive.
 26. Theelectric heated underbody support, heated mattress or heated mattressoverlay of claim 23, wherein the flexible heating element conforms tothe contours of the body of the patient.
 27. The electric heatedunderbody support, heated mattress or heated mattress overlay of claim23, wherein the edges of the heating element include a first side edgeand a second side edge; and a first conductive bus bar coupled to theheating element and extending alongside the first side edge of theheating element, the first bus bar being adapted for coupling to a powersource for powering the heating element; and a second conductive bus barcoupled to the heating element and extending alongside the second sideedge of the heating element, the second bus bar being adapted forcoupling to the power source for powering the heating element; and theheating element is stitched to the first bus bar with a first row ofelectrically conductive stitching; and the heating element is stitchedto the second bus bar with a second row of electrically conductivestitching.
 28. The electric heated underbody support, heated mattress orheated mattress overlay of claim 27, further comprising: a firstelectrically insulating member interposed between the first conductivebus bar and the flexible heater and being secured therebetween by thefirst row of conductive stitching, the first electrically insulatingmember preventing direct electrical contact between the first conductivebus bar and the flexible heater; and a second electrically insulatingmember interposed between the second conductive bus bar and the flexibleheater and being secured therebetween by the second row of electricallyconductive stitching, the second electrically insulating memberpreventing direct electrical contact between the first conductive busbar and the flexible heater.
 29. The electric heated underbody support,heated mattress or heated mattress overlay of claim 23, wherein theheating element has a surface area of generally uniform electricalresistance per unit area such that the heating element produces asubstantially uniform watt density output across the surface area whenthe element is electrically powered; and further comprising: atemperature sensor coupled to the heating element at a first locationthereof where the heating element is configured and located to be inconductive contact with the body of the patient during warming, thefirst location defining a first temperature zone of the surface area ofthe element; and a temperature controller coupled to the temperaturesensor; and an electric power source coupled to the heating element andto the temperature controller, the power source being controlled by thecontroller, according to a sensed temperature of the first temperaturezone, as sensed by the temperature sensor, in order to maintain a firsttemperature of the first temperature zone lower than a secondtemperature of a second temperature zone of the surface area of theheating element, the second temperature zone being defined by a secondlocation of the heating element that is not in conductive contact withthe body during warming.
 30. The electric heated underbody support,heated mattress or heated mattress overlay of claim 23, furthercomprising: a catalyst to accelerate hydrogen peroxide decompositioncoated on or impregnated into an element within the shell, or on theinterior surface of the shell.